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Posts by tangent

In case it isn't clear from the above, you should be measuring 1V across R10 if it's 1k to achieve 1mA through the resistor, not 1mV.
 The documentation doesn't tell you to expect that you can do that. It says, "If R10 is 1 kΩ, then each volt of drop across R10 equals one milliamp through the cascode." 1 mV across a 1 kΩ R10 would mean one microamp of current through R10. This is a simple application of Ohm's Law: I=V/R, in this case.  So go through the troubleshooting guide, as directed by the docs.  What are the measurements on its test points? Specifically: AC voltage between TP1 and TP2 DC and AC...
It's already explained in the docs.
If you're going to use the 50k anyway, and your 100k pot sits down on the board's existing pads, don't bother installing the 100k; wait for the 50k to arrive. Swapipng a 6-pin DIL board-mount device without exposed pins is a royal pain. You stand a good chance of destroying your board.   If the 100k pot would be connected via wires, that changes everything. Now your replacement problem is six independent wires, which is a much simpler task.
There are a whole bunch of tests given in the docs, here. What are the test results?   What do you mean by "no voltage"?  No voltage across what, and at what setting on the meter? I can give a wild guess that you mean DC voltage across R10G, but you aren't actually saying that.
 This is true.  However, it does seem to be a legitimate mystery, rather than something like some meaningless process variation.  I recommend that you pursue it only if you would be gratified to know the answer.  If you don't care why it's happening, don't waste your time. :) Rotating the buffers was a good test.  I should have thought of that myself. You've already rotated the op-amps, which means you're now down to the passives.  That's only likely to find problems in...
 The only reason we expect the ground channel's DC offset to be lower is that it's always unity gain, whereas the other channels can be higher, which magnifies any inherent DC offsets. Given that all three of your amp channels are G=1, I'd expect them to all be well under 20 mV.  If you're changing OPAG and nothing changes, then the problem almost certainly isn't the op-amp, since there are manufacturing variations in op-amps that ensure variable DC offset. I would measure...
 It's especially easy in this case, since solid tantalums typically have their positive lead marked, while alum elecs have their negative lead marked. I've also heard that some LEDs are marked "backwards" compared to the standard way. Bottom line, always check the data sheet.
We have so many different capacitor types because they each have their advantages and disadvantages. Typically the only thing that can replace a tantalum is an aluminum electrolytic, which is much more susceptible to heat, a serious consideration for that particular cap, being right next to a voltage regulator.   Cap types that aren't still useful typically get dropped from the manufacturers' lines. Tants are still being made despite the difficulty of getting the...
 I would be happier with that procedure if you had a known-good instance in the group for comparison. As you say, it is possible that you could get them all backwards.  I doubt it. I would guess that the regulator isn't regulating for some reason, so that the full rectified DC voltage is getting through, and that voltage is too much for the cap. If that's an LM317 you've got bent partly out of the frame, I would cut the remains of C8 off the board then power it back up...
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