Yamaha 1020 distortions in both channels

[stozek2000]

Hi, I've got a problem with Yamaha CR 1020. The receiver was damaged, there was a lack of -25V voltage and I manager to fix it. It worked fine for the next couple of days and the next issue appeared. Just after I turn it on everything is fine, but after a few minutes the signal is very distorted (the same issue in both channels). You can find the oscilloscope record on the video on YouTube. I also did the preamplifier measurements and marked on the picture the moments where the signal starts to be distorted. I just wanted to know if that would be the fault of the adapter (event hough both +-25V voltages are fine). Did anyone of you have a similar issue? Any help appreciated Thanks

 

[avionic]

Does it distort in tone control by-pass ?

 

[avionic]

Does the low and high filter have any influence on the distortion ?

 

[stozek2000]

Distortions are behind the tone control. High filter does impact these distortions, when it's in the position 0 then distortions are most noticeable eg. signal of the tuner. And on the sine wave there are no significant differences between the positions.

 

[clinic-audio]

OK
1) did you try to use it with preamplifier separate from main amplifier (switch behind the unit )?
2) do you have trouble at the output preamplifier sockets ?
3) do you have it with main amp only ?

 

[stozek2000]

1. Yes, already tried it
2. Yes, the signal is distorted at the preamplifier output
3. Power amplifier is fine
I'm quite sure there is an issue with the preamplifier, but no idea if I should check the +-25V adapter or the preamplifier itself. When I turn the receiver off transmitter plugs are sparkling and the sound is distorted from speakers. All electrolyric capacitors have been changed.