How can I know if ICs are bad?

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Hello,
I would like to repair amplifier from old records player.
One channel is silent (you can hear silent buzz and static), other one is silent too, but it starts to "fart" when volume is over 3/4, I can tell that it`s making sounds to the rhythm of music.
I repleaced all the capacitors and measured that ICs are getting right voltage.
I swapped ICs from one channel to the other, but "farting" stays on the same channel, and other one stays silent.
I tried to apply signal after the pots, but nothing changes.

What can I try else? It`s a very simple circuit but is driving me crazy.

In schematic I marked what part of circuit I`m working on (preamp is not on this circuit).
amp.jpg

Thank you for help
 
ICs are bad!
It turned out that I tought that I swapped ICs from one channel to another, but I mixed them up and soldered them back to original places...
Now I swapped them and channel behavior turned around so yes... they are bad.
Anyways do anyone now if there are any substitutes to TBA641B12?
 
Could you isolate the input to the output stage (chipamp) and insert a new PCB with a modern chipamp?
Yes, I could, but I would like to fix this one. The records player was sitting in basement for many many years, but I can remember as a kid, this amp sounded really nice, it reached full volume without any distortion and it was loud. Nothing like cheap modern amplifiers...
 
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