Okay... I have some results...
1) Another capacitor trick by connecting the capacitor from the small blue 100 Ohm resistor array pin 4 or 8 to the INA2137 pin 8 and bypass most of the path. It's very unlikely that both INA2137s could be damaged, but possible I guess.
This seems to have not done anything, for either front or rear.
2) We could also place the capacitor between the INA2137 pins 8 & 9 as a quick test too.
I get some fain, muddy output on the rear, nothing on the front.
3) Another capacitor trick by connecting the capacitor from the small blue 100 Ohm resistor array pin 4 or 8 to the emi filter bottom pad.
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.
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