[Kenwood] RE:TS-940 missing Resistor 152 on IF Board, anyone know why and What is the correct FET direction?

[KD5NWA]

It's quite common in electronic devises to have missing components, an 
engineer will sometimes put optional components that may be required if 
they have to switch to an alternative device. If they install the 
designed device then those extra components are not required. If the 
board is flow soldered then those wholes will have a perfectly smooth 
coating of solder.

Fets for the most part have interchangeable source and drain, but this 
is not universal, while it may work at low frequencies, the gain, 
dynamic range, and distorsion may suffer with most of them. Most have 
interchangeable leads if and only if you do not need maximum 
performance. By comparing the schematic to other copies of similar 
circuits you should be able to determine which is wrong, the schematic 
or the layout diagram. In most cases I would place my bet on the 
schematic being correct, that gets gone over a lot more than the parts 
drawing.

All this talk about Kenwood is making me think, if this rumor is true 
and it becomes official then the price of used Kenwood equipment will 
most likely go up. I would like to buy a TS-850, or a TS-950 while I can 
still afford it. I own a TS-830 and the receiver is fantastic, I've 
never played with a TS-850 but I've always heard that it's even better.


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
>  
>
-- 
Cecil
KD5NWA
<www.qrpradio.com>

'Never argue with an idiot. They drag you down to their level then beat you
with experience.'               -anon