Strange behaviour when setting the bias..

[sonci]

I just fixed my Victor ax-z921 (JVC Ax1010TN), with blown output, and some resistors, now everything seem to work ok. I replaced the output on both channels with some Onsemi, even though only the left channel was burnt. I replaced some caps too, but most were ok.
I set the bias to 10mv for both channels as per manual when the amplifier is in the operating temperature.
The problem is that when I turn on the amplifier from cold, the bias on the left channel start to rise quickly to 18 or 19mv, then after 20 minutes goes back to the normal 10mv and stays there. How is this possible?
ChatGPT suggested that the bias transistor was not touching the heatsink, so I replaced the thermalpad on that but still the same.
Is it risky to use it anyway, the bias stabilize after some time? This amplifier has also a SuperA chip, that may be the problem but I have no way to troubleshot it, unless I find another to replace.

 

[eiraved]

Are the bias transistors on the same heatsink or different? I do think you don't have a problem if the bias goes to normal and remains there.

 

[sonci]

Are the bias transistors on the same heatsink or different? I do think you don't have a problem if the bias goes to normal and remains there.

Yes, on the same heatsink.

 

[sonci]

The right channel is normal, it raise to the set value and stops, both channels play normal.

 

[eiraved]

I would just montor it for a few days to ensure it settles to normal bias and then remains there. If it does remain normal, I wouldn't be concerned about that anomaly.

 

[dr*audio]

You have sine new transistors on the left channel with higher Beta. All is good.