Okay... I have some results...


This seems to have not done anything, for either front or rear.


I get some fain, muddy output on the rear, nothing on the front.


Music! This works for both front and rear.

I tried going back to the top pad of the 100 ohm resistor on the front, which also works.

Going to the bottom pad of the 100 ohm resistor produced a loud tone, and then, after removing the cap, continuous audio, but at a reduced volume compared to when using the top pad of the resistor. The same trick with the rear produced a tone, but at much lower volume, and I get intermittent audio, at an even more reduced volume than the left.

Going back to the black tantalum does nothing to improve things.

I broke out the multimeter again, and checked out the top row (farthest from the INA2137 chips) of resistors. Working left to right (as in the photo), I get (1) something alternating between 100k+ and no continuity, (2) 164 ohms, (3) same as #1, (4) 100 ohms.

Something tells me that's not right.

Okay... found a 100 ohm resistor in my parts bin, and used it to bypass #1 and #3, which gives clean audio again. Looks like we've found our culprits! I'll see if I can get one of our engineers to replace them.

Any idea why these would go bad, and if there's anything I can do to prevent it in the future? edit: could this be a result of the bad ground connection on the amp, that you mentioned in your earlier post?

Cheers,

10 minutes with an iron, and everything works perfectly again.

Thanks to everyone who chimed in, and especially Ross for walking me through the troubleshooting.

Congratulations.

Thanks so much for your detailed and thorough troubleshooting. I've had the same problem for years now and it's driven me crazy, but I just didn't have the know-how to narrow it down. Hopefully Stu will be able to revisit this along with a few other problems that have cropped up.