Kenwood TS-140S SSB/CW TX fault

[VK5ZEA]

Hi Everybody,

I've recently come into possession of a Kenwood TS-140S transceiver. While it has been well loved, it's had a rough life... in the past it has been a field operations radio.

Given it's age it could probably do with an thorough electrolytic capacitor replacement and a general alignment... but it has one immediate serious fault that I have to fix.

There is no transmit (RF output) on SSB or CW on any band, receive is fine on all bands as is transmit and receive when switched to FM.

I initially though that the sliding mic gain control might be faulty, but this does not explain why CW has no RF output.

I'm wondering if there are any Kenwood gurus on here that might point me in the right direction.

73

Michael.
VK5ZEA

 

[VK5ZEA]

Further to my original post and in response to some private messages :-

AM also shows the same symptoms as SSB/CW... receive is OK, no transmit.

I have also done a CPU reset (hold A=B while turning on), this did not change the symptoms.

 

[VK5ZEA]

OK... another follow up...

Contrary to my last message, AM mode does transmit... but with no modulation. FM and SSB/AM audio follow slightly different paths through the radio.

I've found a service manual and am scouring it for possible clues.

 

[popnokick]

Wirelessly posted (Mozilla/5.0 (iPhone; CPU iPhone OS 7_1_1 like Mac OS X) AppleWebKit/537.51.2 (KHTML, like Gecko) Version/7.0 Mobile/11D201 Safari/9537.53)

Examine closely and test the xmtr RF final output transistors. I worked at a Kenwood dealer when that radio was in its heyday, and blown finals was a common repair done by our shop. Your service manual will have the details of where they are, what they are, and how to test.

 

[VK5ZEA]

The RF final is OK in this radio.

My TS-140S works fine on FM transmit, perfect audio and plenty of RF, ~50 Watts out on FM... a little less on AM but no modulation on AM.

 

[VK5ZEA]

OK... time for an update!

I found a dry joint in the general area of the 2nd mixer components which seems to have fixed the SSB modulation problem!! I went over all the boards with a fine tooth comb. Found more dry joints in the LPF board.

This radio transmits quite OK now.

The next major hurdle is that I need to find replacement slider potentiometers for the Pwr, Mic Gain, RF Gain & NB level controls. The Mic Gain one has a "noisy track" around the bottom half of it's travel. I think it would be prudent to replace all four (and get some spares).

Does anyone in here know where I can find replacements to suit the Kenwood TS-140S? I've searched through the Alps and Bourns catalog and can't find anything that would be a direct physical replacement.

It's a shame that an otherwise successful radio repair is being held up by a couple of impossible-to-get parts.

73

Michael.
VK5ZEA