KENWOOD TS-940 PAGE
One of the greatest transceivers ever
produced.
This page provides:
· Some information not available
anywhere else which should be useful to any TS-940 owner,
· Information at single web site, easy
to follow, [no other site provides this about the
940]
· Information remaining available so
more TS-940s will be repaired + functional, (and probably improved),
Version 2: 4 April
2005, Version 3: 25 April 2005, Version
4: 27 May 2005, Version 5: 31 May 2005, Version 6: 10 June
2005: Version 7:
16 June 2005: Version 8:
25 July 2005, Version 9: 30 July 2005. Version 10: 4 August 2005, Version 11:
13 Sep 2005, Version 12: 18 October 2005,
Version 13: 23 October 2005,
Version 14: 22 March 2006, Version 15: 8 April 2006, Version 16: 27 May 2006, Version 17: 12 July
2006
Version 18: 22 Aug 2006,
Version 19: 23 Sep 2006, Version 20: 5
October 2006, Version 21: 7 Jan 2007, Version 22: 17 Jan 2007, Version 23: 5
Oct 2007,
Version 24: 19 April 2008,
Version 25: 27 July 08, Version 26: 20 Sept 08, Version 27: 26
Sep 09,
The intention is to acknowledge the person who
discovered the information
When information is already well documented and
reliably maintained on another site then a hyperlink is made to that site to
avoid yet another slightly different version.
I will publish all email feedback of new
information at the end of the page, so that whatever is discovered by others
can be shared by all. Please email to jaking@es.co.nz
Yours sincerely
Jeff King ZL4AI / DU7 http://www.jking.kol.co.nz/ZL4AI.htm
Disclaimer: No liability or responsibility
whatsoever is taken for any of the information on this site. You assume total
liability for any modification you undertake.
Copyright to Author: Everything on this
page
See also TS-950sdx page which hold valuable
information: http://homepages.ihug.co.nz/~jaking/TS-950sdx.htm
INDEX
ALWAYS
READ THIS SITE TO SEE THE UPDATES PLANNED TO BE PUT ON THE SITE SOON
HUGE
ADVANTAGE IS YOU CAN STILL SERVICE THE 940
KEY
TO Servicing is: HOW TO READ THE SERVICE
MANUAL
HOW
TO FIND FAULTS AND FIX THE RADIO
RECEIVER
PERFORMANCE IMPROVEMENTS.
R1.
KENWOOD PRODUCED 3 SERVICES BULLETINS which do considerably improve the
receiver.
RECEIVER
2. FIELD EFFECT TRANSISTORS AROUND THE WRONG WAY.
RECEIVER
3. THERE IS NO AGC TIMING CORRECTION
SUMMARY
OF R149 AND R150 MIS-LABELLING..
Mike
KC8ZNW on 25/4/05 describes this same behaviour to the Kenwood.net.
Independent
Feedback on how Receiver Improves
THE
PRODUCTION MISTAKE DESCRIBED:
ACKNOWLEDGEMENTS
TO PERSONS WHO HELPED SOLVE THIS
COMMUNICATIONS
WITH KENWOOD JAPAN BELOW:
RECEIVER
4. PIN DIODE IMPROVEMENTS
4.1:
Background on how Pin Diodes were discovered to improve radios.
4.2
RadCom Technical Topics explains what Pin Diodes were supposed to achieve.
Intermodulation
properties of switching diodes, by Dr. Ing. Jochen Jirmann, DB1NV
To Access tHE
SECTIONS Below click here ------>:
www.jking.kol.co.nz/ts-940_02_part2.htm
4.4 Experience from Persons who
modified the TS-940
4.5 : Pin Diode Modification for
TS-440
4.6: So summary of Pin Diode Modification
RECEIVER 5: S METER SLAM AND
IMPROVED PERFORMANCE
6.1 Observation of the Phase Noise
problem by Thomas Hohlfeld DF5KF in 2005
6.2 Extensive History of the Phase
Noise Issues upto about June 1987
6.3 Data Sheet for Problem BA718
OpAmp
6.4 What is Phase Noise and how to
measure it by John Grebenkemper, KI6WX
6.5
Phase Noise measurements on Elecraft K2 by John Grebenkemper, KI6WX
6.6 Significant Phase noise
improvements developed by Thomas Hohlfeld DF5KF
6.7 Information on Ultra Low Noise
OpAmps available in 2008
6.8 Further assessment and Phase
noise improvement evaluations planned by Jeff King ZL4AI
PLL BOARD
0: Reseat Connectors
PLL BOARD
1: Remove the Black Foam from Behind the Board
PLL BOARD
2: Remove the Wax from the VCOs.
PLL BOARD
3: Identify which PLL is not locked
PLL Board
4: PLL Board and RF Board and PLL out of
lock
PLL Board
5: PLL Board and setting voltages
VOLTAGE
REGULATOR HEATS UP AND CAUSES A SHIFT IN BFO ON IF BOARD
COOL AVR COMPONENTS BY REMOUNTING ON HEAT SINK
Power Supply HEAT SINK RUNS TOO HOT
VERIFY THERMISTOR 101 IS ATTACHED AND FUNCTIONING
REPLACE Q101 AND Q 102: THE MOST DANGEROUS DEFECT OF
THE 940
SAFETY PROCEDURES WHEN Q101 AND Q 102 HAVE FAILED:
MOTOR BEARINGS GUMMED UP: TEMPORARY FIX
VK5KYO includes Larger Computer Fan
and relocated Rectifiers.
28 Volt Crowbar safety circuit for
the TS-940
RF BOARD 1: Board Runs very Hot
TS-930 (and TS-940…) Power amplifier
repair
Alternative replacement for MRF485
Repairing old fluorescent displays
(to brighten up dim digits)
AM MODE: HOW TO VERIFY ITS SWITCHED
IN
Service Manual & Serial Numbers
Identifying When Radio Manufactured
INFORMATION NOT ANNOUNCED by
KENWOOD:
TS-940 AVERAGE OUTPUT POWER SSB
USE OF TS940S FSK RECEIVE FOR HF
PACKET
INQUIRY REGARDING USE OF ADDITIONAL
RECVR.
RE-PROGRAMMING THE CONTROL SYSTEM ON
THE DIGITAL A BOARD
PROMOTIONAL
BROCHURE
ALWAYS
READ THIS SITE TO SEE THE UPDATES PLANNED TO BE PUBLISHED
From: "Vaso Nastasic"
<vaso.yt5t@gmail.com>
To: <
Sent: Thursday, January 04, 2007 9:09 PM
Subject: [Kenwood] TS940S CW
heterodyne tone
Hello from this part of world and HNY
2007! I have problem with ……
Anyone can help?
73s de Vaso YT1XX / YT6XX.
Hi Vaso,
did you find the home page of Jeff King ZL4AI,
http://homepages.ihug.co.nz/~jaking/TS-940_02.htm
Regards, Nermin S58DX
On Behalf Of Lynn Baustian
Sent: Friday, 5 January 2007 2:02 p.m.
To:
Subject: [Kenwood] TS-940S
Does anyone happen to have all the info on Jeff Kings sight saved to a .pdf
It could be invaluable should his sight go down for any reason.
73.....
================================================================
From: jaking [mailto:
Sent: Saturday, 6 January 2007 10:48 a.m.
To: '
Cc: 'Lynn Baustian'
Subject: RE: [Kenwood] TS-940S Page and updates
PDF of TS-940 page, or TS-950sdx page. If you
really need this, print to a printer or a pdf writer
and just print off your own version, Or just save the site as an html. Ihug is very reliable and this site is unlikely to go down.
If that happened I would shift it to another ISP.
Taking a copy in any form is not recommended. because I update the
TS-940 page regularly. I record my notes of working on the 940 on the site
page. After that it takes about 5 minutes to post a new page. That way the site
progressively becomes better.
The reason copies are not so good is they will not include improved /
revised information. It is better to have just one authenticated source of
information. For example I used to get lots of questions about how to follow
circuit diagrams. Since I posted my ideas on how to read, all those questions
seem to have stopped. If you have an old copy of the site you will not have
that information. Ironically the reason I first published the site was I had
collected the information and published it because I could see it would be
helpful to others. Now I have to defend the advantages of keeping the
information in just one place.
In the next years or longer as time permits I intend doing on both a
late and an early 940
1.
phase noise tests,
2.
receiver tests, such as MDS [minimum discernable
signal], IMD3 etc, because no source of this
important information exists for modified or later 940s, [ZL4AI measured on his 20 mil unit MDS CW
= -144 dBm, MDS SSB -139 dBm]
3.
band filter adjustments / alignment
4.
FET 2SK125 reversal with before and after laboratory MDS tests,
to establish what the change in receive signal level is. Plus I intend
telephoning Kenwood USA Amateur radio technical support on 001-310-639-4200,
option 5, option 2, option 1, to find out what the real truth of Kenwoods official position on FET
reversal is? I find it difficult to understand why reversing a single FET should overload or make the receiver unstable? I
anticipate the measured change in MDS due to reversal will be only a couple of dBs.
5.
possibly replacing 2SK125s
with J310s to discover if later (year 2005 made) (of
higher quality manufacturing standard) pre-amp FETs
reduce the noise,
6.
try installing better and additional shielding around the
entire pre-amp sections to block out and reduce noise,
7.
replacing band filter diode switches with relays to
see if MDS and other receiver qualities improve,
8.
Figure out the switching in and out of filters in SSB mode, so I can develop a rewiring of jumpers which
allow switching in the empty CW filter bays while in SSB mode. Then try INRAD, and /
or Kenwood AM 6K wide or other filters as additional or alternative switch ins,
to enable filtering capability similar to the TS-950 and TS-850. [Measure
receiver tests, for various combinations.]
9.
publish audio spectrum graphical outputs of the 940
performance. [Possibly try replacing audio components such as capacitors to
give a more hi-fi higher quality audio].
10.
publish files of 940 performance with and without DSP filtering. Experience so far is 940 plus DSP is an exceptional improvement]
11.
-evaluate and publish information on how to link 2
940s together so as to have and simultaneously use, a second 940 as a dual
receiver,
12.
Information about replacing bulbs with LEDs [published version 23]
13.
Details on 28 volt crowbar circuit to protect the
radio against power supply failure, [base data was
published in Version 20]
14.
An adjustable resistor for activating temperature of
the power supply fan,
15.
More experience on removing the very hot power diodes
off the AVR board onto the heatsink
16.
publish details of all the changes Kenwood made to the
940 between 1985 and November 1986. There are many more changes to the 940 than
those on the published services bulletins.
17.
publish info about filter input of SM-220
to remove ghost signals from 1 MHZ generated by the 940. [Published version 24]
All that information, should be of real interest to any 940 owner. For
that reasons I suggest you keep reading the site.
[If anyone has done or
undertakes any of the above earlier please send your results for publication.
There are definitely more mods that can be undertaken
to improve the 940.]
Jeff King ZL4AI
HUGE
ADVANTAGE IS YOU CAN STILL SERVICE THE 940
Remember the only reason most 940 owners ever
sell, is their radio has now developed faults, and they cannot bear the large
cost of getting another person to repair the radio. So sadly they replace it
with a radio that is working, for economic reasons. Most say if it had not
developed faults I will still be using it because its performance is as good as
all the latest models.
INRAD will soon release the 940 roofing filter [930
roofing filter came out recently].
For crowded bands, the roofing filter should
provide the 940 receiver enhanced performance equivalent to the best current
receivers.
Almost all radios after 1991 have been made using
surface mount technology. The components are very small and difficult to work
on.
For many amateurs servicing these radios is
difficult, and requires soldering equipment with good temperature control, very
fine tips and electrostatic safe.
The TS-940, (and others of the very early 1990s
like the Icom 765, and Yaesu
FT-1000D)
can still be serviced, and most parts are still
readily available at local stores.
You can use standard off the shelf equivalent capacitors,
resistors, ICs and often equivalent replacement transistors. The cost of these
parts is low and they are readily easily available.
The only parts hard to get are ICs specially
programmed by Kenwood [Only a few of these in the 940]
You can buy second hand TS-940 boards on EBay
and elsewhere at very reasonable prices. With second hand boards and parts you
can still obtain every component. Don’t sell your 940… Repair it.
If you like kit sets, you could say the 940 is
like one large kit set, preassembled.
KEY TO Servicing is:
HOW TO READ THE SERVICE MANUAL
this section is
first because it is key to working on the Ts-940. It is not explained in the
service manual.
Once you
understand this you can easily understand the TS-940.
First step
is download the manual from www.mods.dk.com, or other sites.
On page 107
find the BLOCK DIGRAM. This is probably the most
useful diagram in the book because it illustrates conceptually how the radio
works.
It should
have been at the very front of the manual.
From this you can easily follow through where major signals and
functions travel.
Then go to
page 12 Receiver and page 17 transmitter and read through how the receiver /
transmitter functions while following through the block diagram. This will give
very good idea of how the radio works.
Then on page 103 find the overall schematic of the
940. This lays outs out all the major
boards. There is a coding system, to trace between boards.
Now zoom into part of that schematic and look at
example connectors:
Best illustrated by worked example.
On The PLL board X50-2020-00 find Connector
Plug 2.
It has five wires:
Two example traces are shown below;
Wire 1-DA0 shown with a destination tag “CAR-1-DA0”, whose destination is Carrier Board (X54-1840-00)(A/2) Connector Plug 1 –DA0 Wire 8,
Wire 2-DA1
Wire 3-DA2
Wire 4-DA3
Wire 5-UL1 shown with a destination tag “CAR-1-UL1”, whose destination is Carrier Board (X54-1840-00)(A/2) Connector Plug 1 –UL1 Wire 4,
As you can see if you trace along all grouped wires
through on the diagram, the grouped wire line leads from one board to another.
Using this
system you can trace from any part of the 940 to any other part.
On each
schematic or board layout diagram all you have to do is find the Connector Plug Number. Then you can easily trace
through the board.
Page 83 to
89 of the service manual shows every Connector Plug
on every board is listed out with description of its function. This helps
identify what the wire function is doing.
Page 80 and
81 shows the physical location of most boards inside the radio.
WARNING:
Please NOTE: There is no colour coding for wires listed in the service manual.
IT IS VERY SAFE PRACTICE BEFORE TAKING A BOARD OUT TO DRAW A DIAGRAM OF THE
BOARD SHOWING EVERY CONNECTOR PLUG AND THE COLOUR OF EEVRY
WIRE. ONLY DOING THIS WILL GUARANTEE YOU PLUG THE WIRS
BACK IN CORRECTLY. FOR THE IF BOARD AND CONTROL BOARD THERE ARE MULTIPLE WAYS
TO PLUG IN WIRES, AND YOU COULD SERIOUSLY DAMAGE YOUR 940 IF YOU DONOTT DARW OUT WIRING COLOUR
CODE PLUG IN DIAGRAMS.
Using the
above decoding method solved the following problems.
From:
W5EJ
Sent:
Friday, 18 August 2006 7:45 p.m.
To:
Subject:
RE: Need help on 940 Wires
Jeff,
after seeing your documentation on the 940 I thought I'd send you a note and
see if you could help me out.
I
picked up a used 940 and appears whoever had it before me had replaced several
connectors inside the unit with direct solder connections. (yes a mess).
Question.
On the Speaker/internal switch unit (left front top with cover top off) there
are 3 connectors that plug into the right side of the unit. One has three
wires, red orange and black. All three of mine are disconnected and I cannot
tell which connector terminal on the PCB to re-solder them too. (your wires
would be in a connector)
I
don’t have another unit to reference and cannot find any pictures. do you
have any pictures or 940's with the tops off could you let me know in what
order front to rear the three wires are in your connector? (Of the three
connectors on the right side facing the unit this is the connector towards the
rear of the unit and only connector on that board with just three wires) Crazy
question I know. …….
Any
thoughts or help or pictures would be greatly appreciated.
thanks
73 - John (W5EJ)
From: jaking [mailto:
Sent: Monday, 21 August 2006 8:59 a.m.
To: 'jwill@verizon.net'
Subject: RE: Need help on 940 Wires
John,
I
don’t have a TS-940 apart right now.
But it is easy enough to figure out. Down load a service manual from www.mods.dk
Then
on page 103 overall schematic, find those connections.
You
may have to look at board layout middle of p 102 to identify the connector
number and wire letter. Looks like connectors 48 29 and 30. You will see the
letters for each number there.
Then
find the same places on the schematic p 103.
Follow
the wires through on the schematic to see which board and connector they end on
another board.
Find
that other connector inside the radio, and get the colour of the wire from
where it connects to the other board.
Then
use a multi meter to verify you have the same wire at both ends. You would be
best to un-plug the other end connector, before measuring continuity, because
that way you are 100% you are only measuring on that wire only.
Then
you can reconnect.
There
is no color coding in the manual so this is the only
way to decode the wire colours.
For
example ON PAGE 103 YOU WILL FIND 48 LG appears to connect to Switch L-49-LG
Or
28 CV1 connects to IF board 14-CV1
So
find IF board 14-CV1, on the IF board and you will
get the colour of that wire there. Un plug IF board 14-CV1,
and use the meter to verify you have the same wire.
This
decoding systems works right through all 940 connections.
Let
me know how you get on.
73s
Jeff
ZL4AI
From:
W5EJ
Sent:
Sunday, 20 August 2006 6:41 p.m.
To:
Subject:
Re: RE: Need help on 940 Wires
Took
your advise and downloaded the manual, had the unit fixed in 30 minutes. Thanks for the help - John
HOW
TO FIND FAULTS AND FIX THE RADIO
I was
initially lost about what and how to look for faults. Developed the following
methodology. (All suggestions about repair methodology are welcome)
Step 1 is to download a service manual
Step 2: Read how radio works.
Read though the receiver and transmitter written
explanations, and then follow those paths through on the circuit diagrams.
Easiest way to follow through is photocopy
circuit pages and get a highlighter and highlight those paths on the circuits.
Only then you get feeling for where you look to
find a particular fault.
Step 3:
Find the region of the radio responsible for the
function causing your fault,
And locate that on the main wiring diagrams and detailed
wiring diagrams.
Then progressively check every connection and
component.
That is slow and tedious.
Write down every check you made.
By a process of logical and elimination you will
find the fault.
It may take days or weeks, but if you are
methodical you will find the fault.
Step 4:
In suspect region:
-
Do go over and tighten all connectors. These white plugs have metal female
clamps which get stretched open after many insertions. For each pin you need to
take each connector out of the plastic sleeve and clamp it more closed with
small pliers. [Female outers are only designed for so
many insertions. After that they just become loose]
-
Re-solder regions of boards
where suspect components are located.
I would guess this would fix 80% of ts-940 faults, because the connectors and solder joints are
the weak point of 940s
Step 6:
Using a digital volt meter continuity checker,
verify all suspect connections are connected both inside and across boards.
(You can make your own RF
volt meter for a couple of dollars by following articles in the ARRL Hand
book.)
Step 7:
If you can locate replacement board for the
suspect region and try that that will get fault absolutely defined to that
board.
The fastest way and possibly cheapest way to
fix is probably by elimination
All boards on the 940 are plug and play. When
you put in replacement boards there are service adjustments to make afterwards
, before seriously using the radio. But if the board is defective you can
replace it and the radio should spring back to life.
For example your can buy a PLL
and / or Digital A Board on EBay for between $50 and $100 each.
If you have problem in these regions I would
suggest you buy, plug and play to eliminate if it is any of these boards.
You can always sell the boards you don’t
need again afterwards.
You can also probably sell your defective board
as well for the parts on it. [Those parts are valuable to others]
Max cost is one board, plus postage plus eBay
fees.
A lot cheaper than sending the radio away, and
waiting and waiting.
Step 8:
To find the fault, with radio running
- Mechanical connection fault find by tapping
components with plastic non conducting object.
-
Fault that occurs as radio
heats up. Use Freeze spray to cool suspect regions. If fault reappears when
cooled you have found the region.
-
Use a hair dryer to heat up
regions to see if you can make a fault appear or dis-appear,
-
Use shields make of
cardboard around suspect commonest to try and isolate the cooling or heating to
just one of two suspect components,
-
Use digital volt meter to
verify correct voltages shown on circuit diagrams,
-
-Use oscilloscope to verify
correct patterns as shown on circuit diagrams
Step 9:
Progressively replace components in suspect
regions. Except for programmed ICs, You can use alternative parts,
From
Find parts description on parts list in service
manual,
Or more detail at
If you are methodical,
make written notes of everything you do,
re-think about what functions you have verified
are working,
re-read the service manual, re-checking your
understanding,
you will fix the 940.
This maybe safer than the risk of damage during shipping.
RECEIVER
PERFORMANCE IMPROVEMENTS.
R1.
KENWOOD PRODUCED 3 SERVICES BULLETINS which do considerably improve the
receiver.
AGC circuit improvement
http://www.kenwood.net/indexKenwood.cfm?do=DownloadFile&Document=2d13f766bec08d9297b46280e3758b9b95e42da53ae01ebf6db6adb98b2ed832baa0aa033a297d15598713460b315fbb
TS-940S Signal To Noise Ratio Improvement With
Noise Blanker
TS-940S VCO/Carrier
To Noise Ratio Improvements
KENWOOD TS-940S RECIPROCAL MIXING NOISE
In early March I [Rich Maher] talked to someone
at International Radio regarding the reciprocal mixing noise problem with the
Kenwood TS-940S. I had been in the process of installing the fix
described in your newsletter (late 1986 issue) and found that it had already
been installed on my TS-940S (S/N 7100269). The factory installation had
one problem, the resistors used for R120/R129 were color
coded for 900 ohm (close enough to the 1K in the newsletter), but in actuality
measured 465 ohms. Apparently, Kenwood had gotten a bad batch of
resistors from some supplier and had not discovered the problem.
At the time you indicated that was the first
report you had received of the resistor value problem and recommended that I
contact Kenwood. I called them and was told that they had not heard of the
problem before. They also stated that a new fix for the reciprocal mixing
noise problem had been developed and was described in a Service Bulletin dated
March 2, l987. I requested a copy of the bulletin and have attached a copy of
it to this letter for your information. (See Issue No. 76, Pg. 30 and 31
for Kenwood Service Bulletin No. 917 and schematics pertaining to this
subject.)
Since receiving the bulletin from Kenwood, I
have installed it on my TS-940S and found it to make a very significant
improvement in weak signal handling in the presence of nearby strong
signals. I would recommend highly that anyone experiencing reciprocal
mixing problems install the new fix. It should be noted that some of the newer
TS-940S have the fix installed. I was preparing to install the fix on a friends's TS-940 which had a serial number 100 lower than
my own and found that the fix had been factory installed. Apparently, more than
one manufacturing site is used and serial numbers are given to each in
blocks. Consequently, it is possible for higher serial numbers to be
produced at one location without the fix, while another site any have cut in
the fix but is using numbers from a lower block.
The quickest way to verify whether the fix has
been installed is to check R120 and R129 on the PLL
Unit (X50-2020-00). If these two resistors are 3.3 ohms in value [Editor
correction Service Bulleting 917 says 3.3 Kilo-Ohms], the fix is already
installed. Do not depend on the on the absence of C176, C180 or C181 as
an indication, as earlier attempts (factory or field) to correct the mixing
noise problem may have removed these same capacitors. The instructions in
the bulletin state that when making the modifications to the RF Unit (X44- 1660-00), it is easiest to move C132/C133 to
the foil side of the board. As the component side of the section of the RF Unit containing these two capacitors has been filled
with wax, it is definitely not easier. The factory installation of the
fix left C132/C133 on the component side and installed the R154/C193 and
R155/C194 series RC networks on the foil side. This is definitely
easier. As a side note, the installation of the fix took me about 2 hours.
Both the PLL Unit and RF
Unit modifications must be completed before the transceiver is usable. If
you install just the PLL Unit modifications and then
try the receiver, CW signals will should like raw
AC.
I hope the above information is helpful to you
in dealing
with the reciprocal mixing noise problem.
(Thanks, Rich
Maher, WZ4Z,
RECEIVER
2. FIELD EFFECT TRANSISTORS AROUND THE WRONG WAY
In September 2004 PY1NR
announced he had discovered:
-on RF
board Preamp Q10 and
-on the IF board 2nd balanced mixer
Q4,
had been drawn on the circuit boards
and mounted in the reverse orientation to that shown in the Kenwood Circuit
Diagram.
See PY1NR web site www.guisard.com
and
http://www.eham.net/articles/9261
Initially ZL4AI
found it hard to understand this website and actually what PY1NR
had discovered. Starting with the circuit board layouts I tried to draw out the
circuit: What I found was that apparently the FETS
were mounted with the drain where the source was supposed to be and vice-versa.
As FETs normally
allow current flow until the gate has a potential, I wonder if this really
makes that much difference.
PY1NR suggest that reversing these transistors will
provide 10 dB of gain. But this claim does not appear be based on before and
after measurement. It would be useful to have some feedback on whether others
have had much improvement by reversing the FETS.
Garey Barrell
provides Kenwood’s advice
=========================================================
=============================
From:
Sent: Wednesday, 9 March 20055:53 a.m.
To: Kenwood@mailman.qth.net
Subject: Re: [Kenwood] RE:TS-940 What is the correct FET direction?
Jeff -
OK..... Just in from
Kenwood...
+++++++++++++++++++++++++++++++++++++++++++++++++++++
Dear Kenwood Customer:
This information pertains
to the TS-940S component location.
The circuit designer said
the installation of Q10 in the actual TS-940S transceiver is correct.
The PCB view in the
Service Manual is correct too. The schematic is the only section that is in
error. The schematic indicates the drain of one FET
connected to the source of the second FET. The
correct installation is to have the source of one FET
connected to the source of the second FET.
In addition, testing at
Kenwood Communications in
If you need further
assistance, please e-mail us again.
Sincerely,
Kenwood Amateur Radio
Customer Support
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
73, Garey
- K4OAH
From: Garey Barrell [k4oah@mindspring.com]
Sent: Friday, 11 March 2005 7:26 a.m.
To:
Subject: Re: [Kenwood] RE:TS-940
What is the correct FET direction?
Jeff -
OK. I just had a discussion via
phone with the Amateur service department at Kenwood.
The Q4 situation is not quite as
clear. The schematic appears to be correct, (sources tied together
or push-pull,) and the board layout
drawing appears to be incorrect.
According to a tech in
The guys at Kenwood, both in LA and
The big question is, these transceivers have
been working and meeting specs for 15+ years, so who cares!? :-)
73, Garey - K4OAH
===============================================================================
-----Original Message-----
From:
Sent: Tuesday, 5 April 2005 9:34 p.m.
To:
Subject: Re: Ts-940
Hi Jeff,
The website is and will be great.
Will look carefully at.
I have two things to say.
First is that the second mixer Q4 JFET is indeed wrong mounted.
Here are attached pictures, you can use them on
the website.
The PCB traces are symmetrical, the mixer should
be balanced, and as the two
FETs are identical type, the way that they are
mounted is obviously wrong.
As I said, I have reversed the Q4 and the
improvement exist, but it is not
so great as other had reported (the sensitivity
goes improved by 2 to 3 dB)
===============================================================================
After reading Kenwood’s Garey’s and Traian’s
advice, I turned around only Q4 on the IF board.
The result was a quieter receiver. I do not
believe that there was any significant gain increase in the receiver.
I would appreciate (and will post on this page)
emails describing others experience regarding this change.
From Kenwood.net on 25/4/05
Hi
Dale
I also became interested in the RX mod you mention. Before opening my 940, I
decided to first check whether drain and source of the 2SK125
are symmetrical or not. This was easy for me because I own a "dead"
940 RF board as a source of parts for future repair
of my rig.
I collected one of the 2SK125s from this board and
built a source-grounded test configuration with a 5K resistor connecting drain
to +8V. Then, I fed a sawtooth test signal (about -6
to -1V) via 10K into the gate. U(drain) was recorded against U(gate) on a DSO (Tek 468). Thereafter, I repeated the measurement with drain
and source exchanged.
I obtained the characteristical FET
response curves and these were exactly (!) identical in both configurations.
This did not change when the test frequency was increased to 10 MHz. It seems,
therefore, that the 2SK125 is symmetrical.
As a consequence, i decided not to correct the layout
error in my 940.
Like others, I also believe that there is not much to improve. My 940 has an RX
sensitivity of about 0.15 µV (10 dB S/N) on all bands (well, I must say it was
worse until I re-aligned the entire RX). The IP3 is
+18 dBm (I once replaced the band switching diodes by
PIN diodes).
Like others, I often had connector problems after working in the 940 - another
reason only to go into this rig when necessary.
Best 73,
Thomas (DF5KF)
THEN
TRAIAN PROVIDES MORE OVERVIEW
-----Original Message-----
From:
Sent: Friday, 29 April 2005 2:05 a.m.
To:
Subject: Re: FW: ts-940
Regarding the TS940 2SK125 preamp, yes the FETs have
this interesting
feature: for low signal/low freq and/or low DC,
they are symmetric. This is why they are used as passive variable low
resistance/attenuator/switching for low signal with rather good results.
The things are changing at HF/VHF amplifiers where
the interelectrode capacitances became important (do
you remember about neutralising a FET preamp?), and
these are not quite symmetrical, as the devices are manufactured so that the
drain to gate capacitance to be as low as possible for obtaining lower out to
in feedback when used for common source applications... So, even if
symmetrical, why to use it as for having the greatest unwanted out ot in capacitance/feedback? The gain obtained by inverting
the D/S for the TS940 Q10 may be still not high (I
don't intend to do it because of the reason explained before), but the
engineering feel tell us that something is not ok there... And regarding the
second mixer, there it is obvious that it is not ok, even if it works... An
counterexample is also the TS950 (both SD and SDX) which use the same Rx
preamp as the TS940 with 2SK125
and 2SK520 (they are all FET
cascade preamps) but for the 950 it is actually build as shown in the diagram,
no drain/source inverting there (maybe the same for their second mixer), so
which of them is the best regarding this, the 940 or the 950?!
Please let me know if any other new info about
the 940/950.
Tnx,
73,
Traian
PY1NR provides feedback and re-endorses previous
statements on turning the FETs around
From:
Sent: Friday, 17 March 2006 10:51 p.m.
To:
Subject: [ts-940] FET Reversal Fix Notes
Dear Fellow TS-940 users-
Just a quick post to let others know this
information, which you can use as you see fit:
I have now fixed 2 TS-940SATs
according to the findings of PY1NR who first detailed
the reversal of 2 FETs in the TS-940, based on
factory mistakes in the PCB silk-screening. After doing my own radio, I
absolutely found a significant increase in received signal levels, with no
audible increase in noise floor. I wondered why other users were not rushing to
do the fix- and then saw several posts denying the validity of the fix.
However, since I did not effectively document this in a scientific manner, I
could not effectively offer valid 'proof' of the results.
When I mentioned this to one of my RACES group
leaders- who also owns a TS-940- he decided that we would to do the 'fix' to
his unit- but this time, we would document the results using a repeatable local
test signal. The documented results: after each FET
was reversed, we found a 1 S-unit improvement in received signal level using
our local test signal in the 20 meter band, for a total of 2 S-units receive
gain improvement.
Now, there is much conjecture regarding the dB
value of S-units, and other TS-940 users may know what these 2 S-units on the
TS-940 meter mean in terms of dB. Generally, from my research, each S-unit may
represent 5 or 6 dB of signal, which means the fix has increased receive gain
10 to 12 db. Certainly nothing to sneeze at: being able to give one of the finest
receivers made the full scope of RF gain that it was
originally intended to have
- at no cost, and without negative
repercussions? As the bands wane on the downside of the sunspot cycle, and
running only a vertical 10 feet off the ground, I am finding I can use all the
noise-free gain available to hear DX!
At any rate, this was my experience, which I
humbly offer to the TS-940 user community.
Wishing you all good DX!
73,
John, WA2OOB
On
Mar 19, 2006, at 1:53 AM, Jeff King wrote:
John,
found
your report very very interesting.
Despite
all the controversy, some of which I have reported on
http://homepages.ihug.co.nz/~jaking/TS-940_02.htm
I would
appreciate if you could you please confirm you turned one FET
around, ran signal test, identified improvement 1 S unit and then Turned other FET around and ran signal test, identified improvement 1 S
unit?
You
know it would be helpful if Kenwood would actually confirm their view of
whether the FET in correct position results in too
much gain.
hope
to work you one day! and
73s
Yours
sincerely
Jeff
King zl4ai
*From:* John Rotondi,
WA2OOB [mailto:wa2oob@earthlink.net]
*Sent:* Sunday, 19 March 2006 11:56 p.m.
*To:*
*Subject:* Re: [ts-940]
FET Reversal Fix Notes
Hello Jeff!
Very nice to hear from you! Thank you for your
interest in my posting on this topic.
I have seen your excellent website- thank you
for providing such valuable information to the user community. I am still
reading through
all the information regarding PIN diodes, and
may mod my radio in that area as well.
Just a bit on my background: I am a
professional sound engineer, and have been
designing/building/maintaining/operating professional music
recording and TV/Film post production
facilities for many years. When I first did the FET
fix to my TS-940, the results were obvious to my
ears. In doing the second radio with my friend,
we systematically followed these steps to document the results relative
to an external repeatable test signal, independent of band conditions, QSB, etc.:
1) Set up the signal source: my MFJ-259 antenna analyzer with whip antenna, to
generate a signal near 14.200 MHz.
2) Set up the TS-940 with a small whip antenna
on the work table, about 4 feet from the test source.
Note that the MFJ-259
RF test signal is fixed in level, so this would
not be a variable in these tests.
3) Tuned the TS-940 to this test signal,
peaking the carrier reception in USB mode, and recording the maximum
S-meter reading.
Note that I moved the radio around a bit to
ensure that the reading was stable and repeatable, and not sensitive to
relative position.
4) Shut off the test source so as not to
deplete the battery while working on the radio.
5) Reversed the first of the FETs, reinstalled it's PC board, installed the whip
antenna, and positioned the radio as for the original measurement.
6) Powered up the test source, and tuned the
TS-940 to it as before.
There was a full 1 S-unit increase in received
signal level.
7) Shut off the test source.
8) Reversed the second of the FETs, reinstalled it's PC board, installed the whip
antenna, and positioned the radio as for the original measurement.
9) Powered up the test source, and tuned the
TS-940 to it as before.
There was now another full 1 S-unit increase in
received signal level over the previous measurement, giving 2 full
S-units total over the original base reading.
While this is probably not as
sophisticated as if we would have used a Communications Monitor (IFR, Marconi, etc.) or other test system
directly coupled to the receiver, with stepped
calibrated attenuators, and RF voltmeters coupled to
the IF of the TS-940, we felt that it
would be a fast way to have valid empirical
data to verify that we had created an improvement, rather than a disability,
for the TS-940. BTW, post fix listening on air clearly showed the
significant gain improvement.
In listening today on 10 meters on my own
TS-940, I know that this additional gain has brought signals to the readable
level that would
otherwise have not been readable. I have also
done extensive listening tests with extremely strong local broadcast signals to
determine if
this fix has compromised rejection of
extraordinarily strong out-of-band signals, or has resulted in compromised
receive RF or
audio intermod or
other non-linearities resulting from component
saturation, imbalance, or interstage distortion- but
have heard no
such issues. I will mention that my recently
purchased IC-706 MK II (for mobile use), of more recent design and with
some DSP, totally
folds up from same broadcast interference that
has no effect on the 940!
The 940 receive audio quality remains
exemplary. I have been pleased with the results of the fix, and feel it was
worth the effort
to realize the full potential of the original
design intent.
I can only think that some amateurs did not
have the same results because perhaps the FETs
were not closely enough matched to begin
with, or they had other problems, such as bad
solder joints as often found in these units?
I hope this information is helpful to you! And
yes- it would be nice if Kenwood would enlighten us on these issues- but
as the radio is not
a current product, and did quite well even with
this 'defect', they have little motivation to do so.
I will look forward to a QSO
with you on HF!
73,
John , WA2OOB
Editors Note:
John has undertaken some very useful
measurements and it is very useful to have some measurements.
Measurement outcomes could be more factual if a
change in signal to noise ratio was measured by laboratory methods described by
the ARRL. For example MDS.
http://p1k.arrl.org/~ehare/aria/ARIA_MANUAL_TESTING.pdf
http://www.arrl.org/~ehare/testproc/testproc.pdf
If someone could do an MDS noise floor
test before and after the FET swap, it would be more
complete evidence of the assumed improvement.
Garey Barrell sensibly
advises:
Even
a good test, i.e., s+n / n measurements before and
after, or _accurate_ noise figure measurements really wouldn't impress me
that much, since a receiver meeting the Kenwood specs would be limited by
external noise regardless!
I suspect Garey is
correct about the noise floor: This is a less than 0.2 microvolt receiver:
Maybe turning the FETS around produces more noise,
[which of course lifts the S meter] but does it produce any more signal or
better signal to noise ratio?
If first before an FET
swap the S meter was calibrated against a signal generator, then signal
strength against independent signal source measured, then an MDS measured, then
after the FET swap the s meter was again
re-calibrated, then a reading of the independent signal sourceand
separately MDS again would show that it was just not an increase in noise.
I wish Kenwood would behave like a responsible
manufacturer and explain the technical reasons they do not recommend
turning the FETs around.
Have a look at the following links which show
how measuring receiver improvement is a difficult undertaking. Even definition
of what you are measuring requires some considerable reading and comprehension.
http://www.sherweng.com/table.html
http://www.rac.ca/opsinfo/smeters.htm
http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/SMeterBlues.htm
http://www.w8ji.com/receivers.htm
From:
Bruce Bennett [mailto:maritimus49@yahoo.com]
Sent: Monday, 21 September 2009 12:49 p.m.
To: jaking@es.co.nz
Subject: Kenwood TS-940S questions
Hi Bruce
Answers are in text below.
Hello Mr. King -
I was hoping to get some advice from you concerning the 940. I am about to buy a 940SAT from a ham here in Indiana.
…… I am really looking forward to this as I
have read for years about the great receiver and superb audio quality for both
ham use and SWLing, which will be a big part of my
use of the rig.
I am aware of the FET problem and I wanted to ask you about your opinions
about my rig. The serial number is 8,2xx,xxx
and I was wondering what you think about whether I should make an effort to
change the installation of the two FETs.
I do not think not will make
much difference. Cliff of Aavid the well know Kenwood repair expert only found 2 db. He is the only person
I know who has used calibrated spectrum analyser to make the measurement. If
you look at the function of an FET it is and on off
valve like a water tap. It should function much the
same no matter which way round it is.
I will soon do some tests now
that I have a calibrated signal generator and spectrum analyser to prove what the
real difference is.
I am confused about the potential effectiveness of this
procedure. I saw something you wrote several years ago in which it appeared
that there was little difference in gain after the leads were changed. However,
there was also a test engineer who achieved about 5-6 db increase in gain with
each FET making an impressive 2 S unit increase in
gain.
6dB = 1 S Unit
In this time of poor propagation I imagine that could
make a significant difference in being able to copy weak signals, DX or
otherwise.
Yes but if you buy or make an
outboard before radio pre-amp you could add 20 dB difference much more easily.
Good pre-amps are not that expensive.
I would very much
appreciate your comments about this. I should tell you that I was close to
buying an Icom 746Pro for
about the same amount that I paid for the 940. However, I really like the pre-DSP design of the Kenwood and the way that it operates, the smooth tuning and that wonderful audio. One
owner said that the way it sounded for AM shortwave listening was wonderful.
You can add DSP at the outlet end and it helps alot.
That decided it for me. Frankly, I also like the
"bigness" of it. It is very enjoyable to sit down to a large rig that
looks like it is ready for serious operating.
73,
Bruce Bennett K6RQR/9
Bloomington, Indiana
p.s. If there is anything else
that you think I should be aware of concerning the operation of my 940 I would
be glad to hear it.
If I find anything else I
will publish it when found.
I did a calibrated minimum discernable
signal test on my 20 Million 940 last year.
ON 20 meters
SSB it measured 134 dB
CW with AF tune, peaked, measured 142 dB
My 20 mil 940 has no extra CW filters.
ARRL test on a 5 mill with CW
filters engaged gave only 138 dB
Much is made of ARRL tests, but unfortunately they do not specify which
filters or mode was engaged for the test. This makes a huge difference to the
result.
The ARRL
TS-950 and TS-950SDX tests were done different filter
combinations. Hence they are incomparable. Yet many Ham buyers (like I once)
did place far too much weight on that one test result when making their decision.
If you look at Sherwood Engineering’s
site you will see variability between various similar models. I suggest you do
a MDS to verify your radio is operating to spec.
Then if there is a problem
you can work your way through the receiver flow path to identify where
performance drops off. All you need to the test is a signal generator, a step attenuator
and an AC volt meter cable of resolving at 2 KHz or less. Be aware that most
cheap volt meters will only measure AC to 400 HZ and hance cannot be used.
The suspicion without any measured
evidence I hold is that those capacitors are 20 years old now and some may have
deteriorated, and replacement may on some radios improve receiver performance
by returning it to specification.
Hope this helps
Yours sincerely
Jeff King
RECEIVER
3. THERE IS NO AGC TIMING CORRECTION
Short (Simple) Version
of What you need to verify on your TS-940 is the next 5 lines
Leave
R 149 and R 150 in their original positions.
With
the radio upside down and the front facing you,
R149
is on the right of the pair and should be 150K or 68K.
R150
is on the left of the pair and should be 2.2 meg.
If
you want to upgrade (the way Kenwood changed the Service Manual), change R149 to
150K.
Thanks to Dennis WB8WTU who suggested a short Version of what to verify.
Now
If you are interested in the history of this
Verification read the rest of this Section 3,
If you are NOT interested in the history of
this Verification go to Section 4.
======================================================================
This R149, R150 issue was first discovered in about 1986, and is
mentioned in International Radios Bulletins
STOP: This
modification was suggested following Kenwood Japan’s advice, that
“The
I.F circuit diagram was correct and the I.F. board was labelled incorrectly.”
Communications_1_2_with_Kenwood_Japan
Kenwood
“The
I.F circuit diagram is incorrect.
Communication 3
with Kenwood Japan
Swapping
R149 and R150 probably increases sensitivity to similar degree as achieved by
just turning the AGC off
Please review KI4NR’s
email below advising the (Kenwood intended) correct construction was
electrical layout of the AGC identical to the TS-930.
KI4NR advises the rising S meter caused is leaking in C128
and C130. On the Editors radio C128 has been replaced and does not fix the rising
S meter.
When time permits
C130 [and / or other AGC capacitors] will be replaced
and when replacement has been shown to remove the rising S meter this web page
will be updated to confirm that. At that time this section of the web page will
be restructured to separate communications about IF circuit diagram from the
rising S meter problem.
SUMMARY
OF R149 AND R150 MIS-LABELLING
Kenwood appears to
have done the following: Please
note there are 2 mistakes.
1. First
incorrectly labelled the schematic: (with resistor values around the wrong way)
2. Then
incorrectly labelled the PC board [to correct the mistakes on the schematic] so
correct resister values put in circuit.
(For example the
position of R150 was labelled as R149 on the PC Board, which resulted in a 150K
resistor being put at the R150 position.)
Areas in grey below
should be disregarded.
Significantly
improves the AGC timing function: After modification:
- You hear weak signals a lot better.
- S meter with AGC SLOW ON
becomes quite responsive and lively in the region of S1 to S4 signals.
--Before S meter did not move much in S1 to S4
region.
--Before it would take a strong signal to lift the
meter suddenly to S4.
I always wondered why the TS-940 behaved differently to other
transceivers [TS-930S, TS950SDX] which react much
faster over S1 to S4.
Mike KC8ZNW on 25/4/05 describes this same behaviour
to the Kenwood.net.
Hello everyone I have a question about the movement of
my 940's meter. It seems that it
barely moves on some signals which are perfectly readable, other sigs give me 8 or 9 and I
have even heard an occasional 10DB+ movement. My TS830S will give me a 2 or 3 s-unit
increase when I switch the antenna to it for the same signal.
Is this an effect of the sensitivity of the receive section? Or do I have a
malfunction? In
addition my VFO exhibits the occasional hiccup on the
last 2 digits on small movements of
the knob. I understand
this may be caused by solder joints.
TIA, Mike KC8ZNW
Executive Summary of AGC Mod
Its easy to modify a
TS-940S to hear better (or as well as) a TS-950SDX.
When fixed, TS-940
really pulls out those very weak signals.
Simply swapping 2 resistors around, will enable this rig to
hear as Kenwood designed and intended in Kenwood’s original circuit
diagram.
The error is on the IF
board:
Kenwood printed labels
for R149 and R150 around the wrong way!!!
As assembled by the
factory, (the outcome is) in the main signal path, a 2,200 Kilo-Ohm resistor
ends up where a 150 Kilo-Ohm Resistor should be.
Being 14 times larger
the 2,200 Kilo-Ohm resistor (incorrectly) significantly degrades the signal.
Swap the resistors
around and the receiver hearing improves significantly!!!
Kenwood have confirmed
the resistors are in the wrong place. Their emails are
below:
Probably “these resistors in the wrong
place” occurs in every TS-940S produced.
Independent Feedback on how Receiver Improves
1.
From: Ed
[mailto:ca.urso2@verizon.net]
Sent: Monday, 23 May 2005 7:18 a.m.
To:
Subject: TS-940S
worked great! Sure enough,
resistors R149 (68K on my equip) and R150 2.2Meg
had been incorrectly installed by
the Mfr. The board markings for those
resistors were wrong.
73,
Ed
Full email at: FeedbacK_3
2.
From: el34guy@aol.com [mailto:el34guy@aol.com]
Sent: Thursday, 23 June 2005 4:46 p.m.
To:
Subject: agc modification
Hi
Jeff,
I
was looking through the 940 page and found my feedback to you(regarding the AGC modification with resistors 149 and 150) under the
alc setting portion. Im sure I mislabeled
my original email to you on this(think I wrote alc). I am having some
luck with changing out the 2.2 meg for a 1 meg resistor. Im thinking maybe a little lower value might be worthwhile
to test also, like a 6-800k ohm value.
I
know I received another email from you on this but I just wanted to let you
know it looked like my feedback was in the wrong spot on your page.
-----Original
Message-----
From: el34guy@aol.com [mailto:el34guy@aol.com]
Sent: Sunday, 12 June 2005 9:43 p.m.
To:
Subject: Re: alc mod
Jeff
I
thought that mod might be a little better than it was for the alc. It made my radio appear as if it was in fast agc mode all the time. There wasnt
a lot of smoothness in the ssb signal that Im used to. Like I said, maybe something like a 1.1 meg is
worth considering in there. There isnt much room to
solder at all in there. Geez, its tight.
73
Mark
[Editors Note: ZL4AI questions the validity of these observations but has
included them to keep feedback information unbiased. Varying the resistors from
Kenwoods values was never recommended or intended.
With resistors changed around on the Editors 940 AGC
slow is still very much slower than AGC fast.]
3.
-----Original Message-----
From: Michael Feryok II [mailto:mikeferyok@yahoo.com]
Sent: Saturday, 9 July 2005 9:57 a.m.
To:
Subject: AGC Mod
Hey Jeff,
Thanks so much for your TS940
page it helped a co-worker and I today to swap the R149-150 resistors for the AGC mod. Very apparent improvement in noise level and gain.
I can hear stations that are buried into the noise floor now. Mike, KC8ZNW
From:
Sent: Saturday, 9 July 2005 9:53 a.m.
To:
Subject: [ts-940] AGC
mod works great!!
My friend and I did the R149-R150 swap and it
improved the gain and
noise level. Adjusted the VR3 for a proper zero on
the meter and
worked LZ1YE and YV5YMA
right after on 17 meters!
Very low noise compared to before the swap. I highly recommend it.
Thanks to everyone here, and Jeff ZL4AI, Mike KC8ZNW
I'm still debating the transistor gain swap.....????
4.
From:
Sent: Tuesday, 12 July 2005 5:37 a.m.
To:
Subject: [ts-940] Re: AGC
mod works great!!
Hello Mike, I'm having both mods done to my 940 now and I hope the out
come is like yours. I'll post after I get my 940 back and let everyone
know how it goes. I have a very late model serial number which is
20700050 and it still had both mistakes in it, so I hope this will
improve on the already great recieve on the 940. 73
and enjoy your
improved TS-940S. Dale, KD5UVV
--- In
> My friend and I did the R149-R150 swap and it improved the gain and
> noise level. Adjusted the VR3 for a proper zero
on the meter and
> worked LZ1YE and YV5YMA
right after on 17 meters!
> Very low noise compared to before the swap. I highly recommend it.
> Thanks to everyone here, and Jeff ZL4AI,
Mike KC8ZNW
> I'm still debating the transistor gain swap.....????
5.
-----Original Message-----
From: Articles@eham.net [mailto:Articles@eham.net]
Sent: Sunday, 24 July 2005 3:52 p.m.
To:
Subject: [Articles] Improve TS-940 Receiver for Weak
Signals
Posted By KB9IV
Well I finally got around to the AGC
mod. What a fantastic difference.........it also improves CW to my ears. In addition the AGC
mod also seems to improve useable weak sensitivity and decreases distortion.
Forget the "FET
reverse" project. NO difference here, it's not worth the risk and
time.
Best 73,
Bill KB9IV
-----Original Message-----
From: Bill & Becky [mailto:wmarvin@hickorytech.net]
Sent: Sunday, 24 July 2005 4:00 p.m.
To:
Subject: 940 AGC Change
Hello Jeff,
Thank you for the info on the "AGC" correction. What a fantastic difference
here!!
Makes a good 940 a great 940........I can now hear
much better not. I found the FET reversal
change useless...........not worth the bother.
Have a Great Day!!
73
Bill KB9IV .......
6.
http://www.eham.net/articles/11090
7.
-----Original Message-----
From: John [mailto:hydroaction@cfl.rr.com]
Sent: Friday, 29 July 2005 4:03 a.m.
To:
Subject: Your 940 observations
Jeff
I appreciate your efforts on the 940. I have to
say the AGC deal is not quite right. I have work on
more 940 that I can remember. I have known for years the silk screening of the
numbers on the circuit board is wrong. but the resistor placement on the board
is correct. also the service manual is wrong on the schematic. The 2.2 Meg ohm
resistor is in parallel with C-127 .....the 68K or 150K resistor is in series
with C-126 which give you the base line time constant when AGC
switch is in the fast postion. This is the CORRECT
arrangement.
73 John KI4NR
Editors note:
On the TS-930 signal board the
equivalent AGC resistors to R150 and R149 are:
R730 2.2M
and
R710 68K
-----Original Message-----
From: LPC Wireless, KI4NR
[mailto:
Sent: Friday, 29 July 2005 5:39 a.m.
To:
Subject: More Info ... Your 940 observations
Jeff
I forget to add something. When you swap the
resistors around. you are putting the 2.2 Meg ohm in series with C-126. this
effectively removes the Base line time constant to all AGC
positions on the switch including AM even thou the switch does not function
there. That why people say the meter is more jumpy. plus the 150 K or 68 K bias
the gate of Q23 more heavy and allows the receiver to stay more sensitive to
low level signals. if you look at the TS-930 schematic this is the correct
circuit in every way and the way Kenwood intended it to work and how the 940 is
One other thing .....on all the older
940 4, 5 and early 6 mil serial number ...the IF board is
different. The gain distribution in not the same.
8.
From:
Jeff King [mailto:jaking@es.co.nz]
Sent:
Monday, 1 August 2005 8:01 a.m.
To:
'css@kenwood.co.jp'
Cc:
'
Subject:
RE RE: Is your advice Correct about TS-940 R149 and R
150: being in wrong places???
Dear
Mr T.Soranaka
Thank
you so much for your 2 emails sent in March 2005 [attached as below].
COMMUNICATIONS_WITH_KENWOOD_JAPAN About R149 & R150
From
your advice I understood:
“The
I.F circuit diagram is correct about positions
of R150 and R 149 and the I.F. board is labelled
incorrectly.”
Because
your advice was valuable I recorded this to a small web page:
http://homepages.ihug.co.nz/~jaking/TS-940_02.htm
This
has been seen by some TS-940 enthusiasts. It enables one to adjust a TS-940 to
operate as (you advised) Kenwood designers really intended.
A
very experienced Kenwood repair expert from the
With
the greatest of respect to Kenwood Corporation and yourself I ask please:
Could
you please review your advice and advise again if R150 and R149 on the IF Board
should be swapped around to make the TS-940 to operate as Kenwood designers
really intended?
============================================================================
30
July 2005:
Abbreviated
summary of key points in Emails from KI4NR Kenwood
Repair Expert in
When
R149 and R150 are swapped around the AGC does not
function as Kenwood intended.
-
The service manual is wrong on the schematic.
-
The silk screening of numbers on the circuit board are reversed to the
schematic and wrong in relation to the schematic (only).
-
But the resulting resistor placement on the board is correct.
I
believe the silk screening on the 940 IF board is correct and the IF schematic
is wrong.
The
2.2 Meg ohm resistor is in parallel with C-127 .....the 68K or 150K resistor is
in series with C-126 which gives the base line time constant when AGC switch is in the fast position. This is the CORRECT
arrangement.
The
2.2 meg ohm resistors in both the TS-930 and TS-940 sets up the bias to the FET from the 3.2 volt AGC
reference voltage. The 68k or 150k in series with the Cap set up the base time
constant. The other FET switch in for slow AGC on SSB and Fixed AGC on AM.
(R730
2.2M and R710 68K, are the equivalent resistors on the TS-930.) The TS-930 is
the correct circuit in every way and the way Kenwood intended "the AGC of the TS-940" to work.
When
you swap R149 and R150 around. you are putting the 2.2 Meg ohm in series with
C-126.
This
effectively removes the Base line time constant to all AGC
positions on the switch including AM even thou the switch does not function there.
That is why people say the meter is more jumpy. Plus the 150K or 68K bias the
gate of Q23 more heavy and allows the receiver to stay more sensitive to low
level signals.
73
John KI4NR
LPC Wireless
Phone:
386-774-9921
=========================================================================
Mr
T.Soranaka I look forward to receiving your advice.
Yours
sincerely
Jeff
King
9.
-----Original Message-----
From: Customer Service Section [mailto:css@kenwood.co.jp]
Sent: Tuesday, 2 August 2005 6:01 p.m.
To:
Subject: Re: RE RE: Is your advice Correct about
TS-940 R149 and R 150: being in wrong places???
Dear Mr.King,
Please accept my apologies for having supplied
incorrect information.
A very experienced Kenwood repair expert from
the
The service manual is wrong on the schematic.
Yours sincerely,
T.Soranaka
++++++++++++++++++++++++++++
Kenwood Corporation
(
URL: http://www.kenwood.com/
Email: css@kenwood.co.jp
++++++++++++++++++++++++++++
10.
From: John Brush
[mailto:brushj@comcast.net]
Sent: Monday, 12 September 2005 2:29
p.m.
To:
Subject: TS-940S R149/R150 More Info
Jeff,
I absolutely agree with the comments
made by John KI4NR. A rising S-meter reading is due
to a leaking capacitor, and not the incorrect placement of R149/R150. In my
case, I did the resistor swap and noticed that the S-meter’s response was
the same for both the AGC’s Fast and Slow
positions – not good. After undoing the resistor swap, I now had the
rising S-meter problem (a problem I didn’t have before the modification).
In my case, the problem was resolved by replacing C126, the capacitor that is
in series with R150 (2.2M) as shown on the schematic. Per John’s advice,
I also plan on replacing C128 and C130.
I must have one of those old IF
boards, because my S-meter pegs when I turn the radio off.
73, John (WA3CAS)
THE PRODUCTION MISTAKE DESCRIBED:
Below is Page 92 of the Revised Service Manual
Observe that:
-R 149 and R 150
are mounted between almost the same connections. I.e. between the junction of
C127- R148 - C128 - C130 - R156 to-> C126 - Q21 -
Q22
-The difference
being that “additional C 126” is between R150 and C126 - Q21 - Q22
Below is page 93 of the Revised Service Manual
You will notice that R 149 is connected between C126 and
the junction of C126 - Q21 - Q22. That is R149 has been mounted where R 150
should be.
Does putting the 2.2M ohm resistor where the 150 ohm
Resistor should be make a difference. Yes! You bet. Change the 150 ohm back to the direct circuit
and the AGC responds very quickly. [similar to
the AGC in a TS-930]. AGC
could not respond quickly before because it had to wait until C126 charged up.
This is in the heart of the AGC
timing section.
Probably all TS-940s have R149 and R150 in the wrong
place.
================================================================
TO CHANGE THE RESISTORS
Change around is easy.
You will need to take the IF Board out.
The difficult part is removing and putting all the
connectors off / on the board.
Before starting, draw a diagram of the board showing
each connector and position and colour of its wires.
That makes it certain you put the right connectors back
in the right places.
If you don’t draw a diagram you will not know
where all the connectors go back. Some two pin connectors could easily go in
more than one place. That’s could be disastrous
These colours are not shown in the service manual.
I suggest you put in new resistors, because with
longer leads they will slightly easy to hold in place while soldering.
THE INITIAL PROBLEM SYMPTOMS:
ZL4AI discovered this while searching for the a fault described below
AGC:
Only happens in SSB:
If TS-940 left not running for a couple of days, when
you turn it on,
with the AGC turned off or
set in fast position, then the meter needle
goes to up 25db + 9
(approx). The signal is diminished like RF gain
turned up. Over the next 25 minutes the meter needle
slowly moves it way
back to S0.
SSB in normal position, and TS-940 turned on this does not happen.
Needle is initially at s0.
During the first 25 minutes if you switch between off
- fast - normal
then the needle goes back to zero in less time ... say
20 minutes.
If TS-940 left for a couple of months, and then turned
on same behaviour
but worse.
Meter needle goes full scale right in all positions
(off - fast -
normal)
It takes longer say 40 minutes for the needle to move
to the s0. then
ts-940 functions as described above.
=========================================================================
After R149 and
R150 changed back to positions Kenwood intended
in the circuit diagram, the result was:
-The fault of the rising S meter when cold
disappeared.
- S meter dropped back to S1 on both AGC OFF and AGC SLOW, with no
antenna signal. Needed to adjust VR3 to bring
the S Meter to S0.
ACKNOWLEDGEMENTS TO PERSONS WHO HELPED SOLVE THIS
T.Soranaka Kenwood
traian@deck.ro
who diagnosed the problem and really understands these
circuits. Traian appears to have amazing skill and
after reading the symptoms pointed me to look at R149. From there it became
obvious the circuit was not assembled according to the circuit diagram.
Garey Barrell
'k4oah@mindspring.com'
Who provide some very useful advice on functions of
components and explanations how to read the circuit diagrams.
==============================================================
A CAUTION:
Not all IF boards
are identical.
I installed another
IF board installed as per factory spec with R149 and R 150 in their other components
position in my TS-940. It did not have the rising S meter problem. But it was not sensitive to weak signals
==============================================================
COMMUNICATIONS WITH KENWOOD JAPAN
-----Original Message-----
From: Customer Service Section [mailto:css@kenwood.co.jp]
Sent: Tuesday, 15 March 20057:11 p.m.
To:
Subject: Re: Question about TS-940 R149 and R 150: Appear to be in wrong
places!
Dear Customer,
Thank you for your reply. I suppose that currently R149 and R150 are
mounted correctly as the screen printing lettering R149 and R150 are reversed.
Please confirm actual resistors comparing the circuit diagram. The circuit diagram
is correct.
Yours sincerely,
T.Soranaka
++++++++++++++++++++++++++++
CustomerSupportCenter
Kenwood Corporation
(
Email: css@kenwood.co.jp
++++++++++++++++++++++++++++
----- Original Message -----
From: Jeff King
To: 'Customer Service Section'
Cc: k4oah@mindspring.com ; traian@deck.ro ;
Bill Bailey ; Ken McVie
Sent: Tuesday, March 15, 20051:53 PM
Subject: RE: Question about TS-940 R149 and R 150: Appear to
be in wrong places!
Dear T.Soranaka
Thank you for your advice.
Could you please advise if it would be advisable to swap R149 with
R 150 and vice versa, so the TS-940 functions in accordance with the circuit
diagram?
Yours sincerely
Jeff King
-----Original Message-----
From: Customer Service Section [mailto:css@kenwood.co.jp]
Sent: Monday, 14 March 200510:29 p.m.
To:
Cc:
Subject: Re: Question about TS-940 R149 and R 150: Appear to be in wrong
places!
Dear Customer,
We are sorry for inconvnience. I have checked
with our communication department as to R149 and R150. Unfortunately
reference number of R149 and R150 on the borad are
reversed. R150 and R149 are 2.2M and 68K or 150K respectively as shown in the
Service Manual.
Yours sincerely,
T.Soranaka
++++++++++++++++++++++++++++
CustomerSupportCenter
Kenwood Corporation
(
Email: css@kenwood.co.jp
++++++++++++++++++++++++++++
----- Original Message -----
From: Jeff King
To: css@kenwood.co.jp ;
Cc: k4oah@mindspring.com ; traian@deck.ro ;
Bill Bailey ; Ken McVie
Sent: Saturday, March 12, 20056:41 AM
Subject: Question about TS-940 R149 and R 150: Appear to be in wrong
places!
Dear Kenwood Customers Services,
I have found that when emailing Kenwood
Thank you for your recent replies.
While trying to find a fault in my TS-940 I have been going over the IF
board. It appears to me when the board was made it was marked with the screen
printing lettering of R149 being where R150 should be and vice versa. I have
followed the board traces both in the Service Manual and on the back of a
board, and these resistors both seem to be in the wrong place.
This means:
Specified in First Service Manual:
R149 68K
R150 2.2M
Specified in Revised Service Manual:
R149 150K
R150K 2.2M
Resistors as actually installed on my board if you follow the logic of
the circuit diagram.
R149 2.2M
R150 150K
I have two IF boards here and they both have the resistors installed as
required by the screen printing and hence on both boards both resistors are
reversed. Possibly this is the case for every TS-940 ever made.
I cannot understand how the circuits would function as the designer
intended, as the installed resistors are very different to those shown on the
schematic diagrams. Could you please advise if my observation is correct, and
after later when Kenwood has investigated if it would be advisable to
swap R149 with R 150 and vice versa?
At this time could you please just confirm that the question will be
investigated?
I look forward to your reply.
Yours sincerely
Jeff King ZL4AI
RECEIVER
4. PIN DIODE IMPROVEMENTS
This improvement is not fully
documented yet. Please send in information.
4.1:
Background on how Pin Diodes were discovered to improve radios.
[TenTec] Pin Diodes /
Paragon
Chester
Wed, 17 Sep 1997 17:14:45 -0400
TenTec builds a great amateur radio and obviously to give you a 'million dollar radio' that cost the user five bucks, economics really does have to enter the picture. PIN diodes have been around for many years, however they were initially invented, designed, manufactured, and sold to be microwave switching devices, obviously because you can not use mechanical relays for internal switching within a microwave RF circuit. It has not been developed as a 'low frequency' device until within the last 20 years or so.
Dont quote me on this because I've been out of microwave design for too long. A regular diode is a piece of silicon (or germanium) that has a junction. One side of the junction is doped, during mfg process, to have an excess of electrons (+P) and the other side of the diode is doped to have an excess of holes (-N), therefore the term PN junction. And of course a PN junction diode will pass current (a signal) in only one direction. A PIN diode has these (almost) same characteristics (but each side is doped differently than than a standard diode), and in addition, between the +P and the -N sections is a third section that is doped specifically to allow the diode to switch VERY rapidly, and this region is called the Intrensic junction, thus the name PIN. The speed that a PIN diode can switch is basically determined by the width of this Intrensic area, the narrower the I junction, the faster it will switch and therefore the higher the rf frequency that you can pass throught it. Unfortunately, to build a PIN diode that will switch at HF freqs (below 30 MHz), the I junction has to be made wider, or the diode will switch too fast to allow one cycle of an HF signal to pass through it.
What all of this means is that PIN diodes are relatively expensive. A regular PN junction diode (typically a 1N4148 for instance) may cost 5 cent apiece,
however a 'cheap' true PIN diode will cost between one and three dollars apiece; and thats why you do not see them in very many amateur radios.
ECONOMICS. (I'm not sure why it took that much verbage to explain, but it did.)
Corsair II's used a regular silicon switching diode, 1N4148 to switch the filters. The Omni 6 does use PIN diodes, but probably because of the above
mentioned economics, TenTec uses diodes that 'will do the job' verses expensive PIN diodes.
I read Rhode's article on PIN diodes and decided I could improve the IM performance of my Omni 6 (it didn't need it!!), so I bought the expensive Hewlett-
Packard PIN diodes that Rhode stated were the best, and installed them in my Omni 6. Over the past five years using my Omni, chasing DX and participating
in some serious DX contest, I have yet failed to see where these expensive HP PIN diodes made any substantial improvement.
TenTec runs about 10ma of current through their production PIN diodes, in order to gain the full IM advantage of the HP PIN diodes, you must run 80ma
through the HP PIN diodes!
So the bottom line is if you replace the PIN or silicon diodes in a rig, you will see (hear) practically no improvement, UNLESS you redesign the circuitry to
utilize the diodes operating at their optimum design specifications. Probably if you find the filter switching diodes in your rig are running 'hot' to your touch, it
probably means that someone has taken the time to change the current running through the switching diodes to really improve the IMD.
At 01:32 PM 9/17/97 -0400, you wrote:
>H. M. 'Puck' Motley W4PM wrote:
>> I have the feeling that the pin diodes in question are a modification
>> suggested in an article by Ulrich Rhode (not sure of the spelling of his
>> name) a few years back concerning 2nd order IMD in modern rigs. One of
>> the rigs mentioned was the Paragon. The article stated that by replacing
>> the common switching diodes used to switch the receiver front end band
>> pass filters with a certain type of pin diode, 2nd order IMD could be
>> improved. Maybe some of our more technically oriented folks remember this
>> article and can comment in greater detail. This is all I remember so if
>> you have additional questions don't ask me!
>Thanks, Puck. I was certain it was something Rohde said, just wasn't
>quite sure when or what the exact reason was. I just spoke to Ten Tec
>about this, and they actually said they had tested different types of
>diodes to switch the Paragon's receiver filters, and settled on regular
>switching diodes because there wasn't much difference with other types.
>So, I guess replacing the receiver filter switching diodes with PIN or
>other (hot carrier, etc.) types is probably a mod that some users have
>done themselves. At least I know for sure it's not a factory
>modification.
>Is there anyone out there who knows this for sure? Has anyone done the
>aforementioned mod? I know one fellow recently mentioned in a message
>that a rig he had for sale had the mod. Now I'll go search for the Rohde
>article. 8^)
>73, KE3KR
4.2 RadCom Technical Topics explains what Pin Diodes were supposed to achieve.
TECHNICAL TOPICS
April 1995
RF SWITCHING I TUNING DIODES
TT FEBRUARY 1993 REPORTED
briefly an important article by Dr Ulrich Noble, KA2WEU/DJ2LR,
which was published simultaneously in English and German QST
and CQ‑DL November 1992) on
"Recent advances in shortwave receiver design". He subsequently
published a series of three articles (QST May, June
and July 1994)on Key components of modem receiver design, and a recent follow‑up
Key components of modern receiver design: a second look" (QST, December 1994). In these articles he stressed that for
receivers intended to have a very wide dynamic range, the intermodulation
distortion that arises from the use of unsuitable RF
switching and tuning diodes imposes an important limitation. He has recommended
the use (or substitution) of such special‑purpose RF
diodes as the Hewlett‑Packard HP5082‑3081
PIN diodes.
Dr
Rohde's articles encouraged Tom Thomson, WOIVJ, to
investigate how bad in practice are the more distortion‑prone
switching diodes and how good are those designed for low distortion
('Exploring intermodulation distortion in RF switching and tuning diodes', QST,
December 1994). He carried out laboratory tests on four types of diodes: The IN4153 generic PN switching
diode: the Motorola MPN 3700 PIN diode intended for RF switching; the BAT‑17 Siemens PIN switching diode;
and the low‑cost 1N4007 which is a generic 1 kV‑PIV
rectifier diode with a PIN structure but not intended for RF
switching
He
has tabulated results in terms of diode switch insertion loss (dB) at 1O MHz
with 0, 5, 10 and 20mA bias currents; and similarly
the second‑ and third‑order intercept points (IP2,
1P3 and dBm). He draws the following conclusions:
"RF‑specified PIN diodes are the devices
of choice for low‑distortion switching at HF
and above, for band pass filter selection and C switching in a narrow‑band
pre‑selector.
He
adds: 'The manually switched and tuned front‑end filters of the 1960s and
1970s had much to offer in terms of second‑order IMD,
but we need not retrogress to those techniques to achieve improved 1P2 and 1P3
performance today. More attention paid to front‑end filtering in general
can produce the improvement we need."
Dr
Rohde in commenting on W0IVJ's finding, notes that
many amateurs had reported difficulty in obtaining HP5062‑3081
diodes. He recognises that even with the Motorola MPN3700
with a
