Kenwood KR-A4030 intermittent sound both channels

[mauro.madeira]

Can someone help?
My KR-A4030 has an annoying intermittent loss of sound in both channels, but mostly in the right one. It's not a contact fault. When I touch a finger in the terminals of one of the first amplifiers transistors (Q301-Q304) it's like some current is injected and it returns to work fine. After some time the sound fades away in one of the channels, or both or continues to work. I don't have the schematics to help me (would help a lot).

Thanks a lot for any help.

[vtech]

I am not sure if "touching transistors" would tell you a whole lot?
Strictly working out of memory; how about goosing the volume control?
Does it have the same effect when the problem occurs?
I seemed to recall something about the dirty volume control but not sure?
Have a paper manual for 5030 but not sure the difference from 4030?

[mauro.madeira]

Hi Vtech!
Thank you very much for your the help.
The first thing I've thought to blame was the volume control. But it's not.
When I touch the circuit after the volume control I inject 60Hz noise. I here the HUMMM and one or both amplifiers return to sound well. Some times it stays for minutes and sometimes I had to repeat the operation right after to get the sound back.
I have tried to compared the voltage levels between the two left and right amplifiers and could detected no differences.

I really don't know if the 5030 diagram is the same, but externally they are very alike. The 5030 has a three more buttons right of the treble control.

Thank you.

[mauro.madeira]

Vtech,

Thanks to you I have found the problem.

Trying to find the diagram for 5030 instead I came across another forum where someone had the same problem for the 5030.
And the cause is very simple: bad contact inside the relay of output stage!

Just cleaned the contacts and happy I am!

Intermittent problems are always the most difficult to fix.

Thanks a lot!

[vtech]

Glad you got it. Persistence pays.