Mac IIsi internal speaker distortion

[Bolle]

I have a IIsi here and the internal speaker only gives very distorted sound output.

The speaker itself is fine, already tried a known good speaker as well and it is giving the same distorted sound.

Board is clean and recapped. External sound output is working fine without distortion.

Found and fixed a bad trace between the audio op-amp and the transistors driving the speaker but that didn't help.

Transistors Q10 and Q11 check out fine. No other bad traces in the output stage. 12V and -12V are present and stable.

That's pretty much the whole speaker output stage so what else could go wrong and give me distorted sound?

 

[cruff]

Do you have an oscilloscope available?  If you sent a pure sine wave to the speaker you could trace the signal path to see where the distortion was being introduced and narrow down the problem component(s).

 

[Bolle]

Fixed... while the transistors Q10 and Q11 checked out fine on the multimeter they must have been broken.

Swapped them for new ones and the sound is loud and clear again. Makes me wonder what damaged them, they did not look like they got hit by a lot of cap goo.

Might have been that broken trace from the op-amp...