Electronics > Repair
Vintage Kenwood Receiver Volume Issues
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Arty30:
Hello All. I am working on a 69' Kenwood/Trio TK-140X Stereo Receiver. I have done a re-cap since a few tested caps were marginal and some distortion issues were present. The issue that I'm having is that the distortion in the left channel is still present, and seems to be caused by the gain being way too high, which is causing peaking/distortion. If it turn the balance almost all the way right it is balanced and no longer distorted. I have ruled out the main amp which leaves the "tone amp" and "Pre amp" which might not amplify the AUX signal I'm using, its hard to follow the switch diagrams. my question to you is what could make an amp have too high gain? I can think of several ways for too low, but not too high. I'm planning on doing more tests with my signal tracer to narrow down the tone or pre amp, but I'm interested to see if anyone has any insights, Thanks.

I've linked a schematic.

Arty.
wasedadoc:
Feedback loop gone open circuit?

If you have a scope and sig gen it should be easy to compare corresponding points in left and right channels.
andy3055:
It could be a bad ground on the signal path.
David_AVD:
Replace the 2SC458 transistors in the tone amp section as they are known causes of all sorts of problems. You can use KSC1845 in their place, but check the pinout. The face with the text is opposite between the 2 types.

Also check for resistors that have gone high in value.
floobydust:
I would take DCV measurements on the transistors and write them down. Don't slip with the probe. The schematic lists many voltages and you can compare readings between the two channels to narrow down a stage having problems.

I suggest to do a recap of the unit, for something of this age it was out in 1969, I outright replace all the electrolytic capacitors. They'll have dried out, going low value or worse if they short. Hmm I see ads in Playboy for it lol.

Not sure why but the transistors also fail with age, go noisy.
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