/diy/ - Do It Yourself

>>1323415
gets it. 60-90% of electronics engineering is library science

>>1323426
heat might be normal for that sort of regulator design.
if all of TP41-TP46 are correct, then your problem likely lies elsewhere. my wild-ass guess is that one of the opamps U1-U4 got damaged somehow, possibly due to a power surge or to static. U1 and U4 in particular have sensitive inputs
lacking a scope, you might build a probe like Pic related, connected to a small speaker amp (battery-powered is best). if you replace the speaker with a dummy load, you can use this probe to listen your way along the audio path and try to find where that objectionable edge appears. a 120V waffle iron or similar ~1500W non-PTC heating device makes a surprisingly competent 8 ohm dummy load

>>1323444
only the designer of the device knows for sure and he ain't tellin'