[Kenwood] RE:TS-940 missing Resistor 152 on IF Board,
anyone know why and What is the correct FET direction?
Jeff King
jaking at es.co.nz
Mon Mar 7 23:44:00 EST 2005
Garey,
Thanks for the information.
1.
Resistor 152. I have problem with the AGC and I am trying to find out
whether R152 was removed by Kenwood. Kenwood has no office in New
Zealand, so we have to do some of the repair work here whether we like
it of not. I emailed Kenwood USA who asked me to email Kenwood
Australia. I am still waiting on Kenwood to provide expert advice. I see
every reason to follow Kenwood's advice, if they provide it.
>From your advice, I understand that Kenwood did make changes to the
TS-940 but did not publish all the information publicly.
I initially assumed that it was possible my TS-940 got passed Kenwood QA
and out of the factory with parts missing. This seems a real
possibility.
I am trying to verify if Kenwood has published any official information
to show that R152 should be removed. There are at least two 940s without
R152. Maybe there are many other Ts-940s without R152, and if others
reply that will give an indication of whether Kenwood removed this part
without making any public statement.
I am a professional engineer and understand what you are saying about
circumstances varying. I am passionate about Kenwood equipment and have
invested in it because it is quality.
2. Re FETs backwards.
If you look at Eham.net you will see I was initially sceptical about the
PY1NR claim. I understand all Kenwood said was "FET's are correct as
installed". From Kenwood's circuit diagrams I re-drew from scratch the
Circuit board layout. If you do this, you will find that the FETs are
the reverse direction to the direction shown in the circuit diagrams. So
which direction is correct? .... I can not tell ....
As the FETS are reverse to the circuit diagram, how can the circuits
function as intended by the circuit diagram?
Usually in engineering the circuit diagram takes precedence, because it
represents the logic the designer had in mind.
The possibilities are:
- Kenwood made a mistake and drew the transistors in backwards on the
Circuit board diagrams,
- Kenwood deliberately reversed the FETs from the circuit diagrams.
As I understand it, FETs are like valves and not that particular
regarding direction. This would mean it would not matter much which way
the FETS were positioned.
There appear to be at least 5 TS-940s who have had significant
improvement by turning the FETS around. I am interested in hearing if
many other Hams have experienced an improvement by turning the FETs
around. [One cannot realistically say that putting in a pre-amplifier
that does not work as the officially released circuits show it should,
is going to damage the dynamic range and blocking.]
Gary have you got more information on Kenwood's statement about the
positioning of the FETs? If so I would really appreciate to know what
they have officially said.
Yours sincerely
Jeff ZL4AI
-----Original Message-----
From: kenwood-bounces at mailman.qth.net
[mailto:kenwood-bounces at mailman.qth.net] On Behalf Of Garey Barrell
Sent: Tuesday, 8 March 2005 11:38 a.m.
To: Kenwood at mailman.qth.net
Subject: Re: [Kenwood] TS-940 missing Resistor 152 on IF Board, anyone
knowwhy?
Perhaps I'm just too trusting, but I figure Kenwood knows more about
what should or should not be on a particular board than any "field
techs". IF there is a location for a part, and there are burned pieces
sticking up, leads cut off, or otherwise an indication that there WAS a
part there when it came from the factory, then yes, I'm going to find
out what should be there and replace it. When there is no indication at
all that a part was EVER installed there, I'm going to assume that it's
NOT supposed to be there. I've been working in this field long enough
to know that there are "post-production" changes that sometimes call for
removal of a part. It might be due to a device change, circuit change
or other perfectly valid reason. Engineers aren't perfect, and
circumstances DO change. You may also find parts soldered on the "back"
of a board for the same reason. Sometimes it's because a vendor has
made what to them was a "minor" change in a device, but it happens to be
a "critical" change in your particular circuit. Sometimes the
variations in production show a trend that calls for a change, but not
significant enough to warrant a redesign of a PC board.
Assuming you trust Kenwood enough to spend a couple thousand bucks on
one of their products, I think you should trust that your unit passed
final test, and meets published specs. If you aren't comfortable doing
that, then perhaps you should buy another brand.
As for the "great backwards FET conspiracy", Kenwood has specifically
addressed this point and stated that the FET's are correct as installed
for the specific units they are installed in. They do NOT advise
reversing "your" unit to match some documentation that may or may not be
correct for your particular unit. This is akin to the old trick of
putting a preamp in front of your receiver. The S-Meter reads "10 dB
higher" than it did before, so it must be helping, never noticing that
the background noise came up 20 dB and the dynamic range and blocking
went to pot.
73, Garey - K4OAH
Atlanta
Drake C-Line Service Manual
<http://hr99.home.mindspring.com/R-4C_Servicez/>
Jeff King wrote:
>Dear Traian YO9FZS
>
>I am really impressed a grateful with your reply. Thanks very much.
>
>1. Clearly in your photograph C159 and R152 is missing on your board.
>
>2. Re circuit diagram. In my First Edition paper copy of the service
>manual.
>It shows R118 as 4.7K between Q13 and L17 to C96
>
>Then in Revised Edition service manual (I got off the internet), and
you
>are right R118 has been removed from the circuit.
>Kenwood never mentioned this in any of the Service Bulletins I found on
>the internet.
>
>Unfortunately neither service manual states a publication date
>
>
>3.
>R152 is:
>- in First Edition service manual,
>- in Revised Edition service manual,
>- not on my IF Board Serial number 6030687 imported from USA
>- on my spare IF board from Serial number 7xxxxxxx imported from USA.
>
>4.
>C129
>- in First Edition service manual,
>- NOT in Revised Edition service manual, [R153 is now drawn where C129
>used to be drawn]
>- not on my IF Board Serial number 6030687 imported from USA
>- on my spare IF board from Serial number 7xxxxxxx imported from USA.
>
>
>I am still not convinced that R152 should be missing.
>I agree it maybe more than a coincidence that it is missing on both our
>boards dated 1985 and March 1986. Apparently Kenwood assembled radios
at
>different assembly plants. Some assembly plants did modifications
before
>other assembly plants. So it is possible to have a later serial number
>radio without factory modifications, where an earlier serial number has
>the factory modifications.
>
>I will wait to see if anyone else knows about why Resistor 152 is
>missing.
>
>Have you tried the PY1NR reversing of the field effect transistors? If
>so did produce much gain for you?
>
>Yours sincerely
>Jeff ZL4AI
>
>
>
>
>
>-----Original Message-----
>From: Traian Belinas [mailto:traian at deck.ro]
>Sent: Tuesday, 8 March 2005 5:03 a.m.
>To: jaking at es.co.nz
>Subject: Re: [Kenwood] TS-940 missing resistror on IF Board, anyone
know
>why?
>
>Dear Jeff,
>
>I have bought used defective TS940SAT from VE and had repaired it.
>I took some pictures during that time.
>Your post made me curious, and as no one had answer yet, I have checked
>here
>and the following are my findings regarding it:
>
>1) Looking on my service manual (W7FG copy), I could find a R117 at Q13
>source and a R119 at Q13 drain resistors on the IF unit diagram, but
>could
>not find a R118 at that stage on the diagram (but had no time for
>looking
>very carrefully at other parts of the IF Unit diagram).
>
>2) Looking on the same diagram, I could find R152 at D49 cathode but
not
>the
>C129 (it shall be at the Q21/Q22 AGC detector/amplifier stages, but it
>isn't).
>I have found a picture I had take from the IF unit during the trcvr
>repair
>and searched carrefully for the C129 and R152.
>I had cut the interresting part of it, it is attached here; zoom out
>for
>better seeing it. See that the places labeled C129 and R152
>respectivelly
>are empty; the place marking and the holes for the C129 can be seen.
>The R152 and the C129 are not fitted on my TS940 IF board indeed, even
>if
>the R152 apears on the diagram/schematic.
>
>So, all of your findings are confirmed and I don't think that these are
>manufacturing problems, but rather mods implemented during the
>manufacture
>or Service Bulletins.
>
>The serial number of my 940 is 602xxxxx, a some early one (the oldest
>are
>5xxxxx S/N '83 manufacture and the latest are 1xxxxx '89 manufacture
>date)
>but I saw that it include some mods (including Kenwood Service
>Bulletins),
>some of them made by previous owner.
>
>Hope this to be of help to you.
>
>GL & All the Best,
>Greetings from Bucharest, Romania,
>73,
>Traian, YO9FZS
>
>
>jaking at es.co.nz wrote:
>
>
>
>>1.
>>While looking for a fault on the IF Board , I noticed that Resistor
>>
>>
>118
>
>
>>in the 4th IF amp is missing, and foil is soldered over indicating it
>>was never installed.
>>
>>When I checked on another IF board, (I have access too) Resistor 118
>>
>>
>has
>
>
>>also never been installed there.
>>
>>Does anyone know if Kenwood deliberately missed Resistor 118 out? or
>>removed it?
>>
>>2.
>>I have also found Capacitor 129 and Resistor 152 missing from this IF
>>board. These seem like serious mistakes during production and I will
>>
>>
>put
>
>
>>them back in unless anyone can explain why they are missing.
>>
>>Has anyone found that some TS-940s come with components missed out
>>during production assembly: If so could you please tell which parts
>>
>>
>are
>
>
>>not installed.
>>
>>I would appreciate all and any comments.
>>
>>Yours sincerely
>>
>>Jeff ZL4aI
>>
>>
>
>
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