[Kenwood] RE:TS-940 What is the correct FET direction?

Tue Mar 8 00:16:19 EST 2005

Rob,

Thanks for your interest.
The original FET posts are:

www.guisard.com

http://www.eham.net/articles/9261

Read them in this order.

My sketches of the drawn out board circuit are not good enough quality
to post, and I do not have time to re-draw them right now.

If you take the circuit diagram in the Service Manual and re-draw out
you will see the FETs are indeed the reverse way around. 

Yours sincerely
Jeff King

-----Original Message-----
From: Rob Frohne [mailto:frohro at wwc.edu] 
Sent: Tuesday, 8 March 2005 6:04 p.m.
To: jaking at es.co.nz
Subject: Re: [Kenwood] RE:TS-940 missing Resistor 152 on IF Board,
anyone know why and What is the correct FET direction?

Hi Jeff,

All this talk about the FETs and R152 has me curious.  Could you post 
the circuit diagrams somewhere?

73,

Rob
On Mar 7, 2005, at 8:44 PM, Jeff King wrote:

>
>
> 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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--
Rob Frohne, Ph.D., P.E.
E.F. Cross School of Engineering
Walla Walla College
http://www.wwc.edu/~frohro/