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Posts by tangent

I'm not sure exactly what you mean, so why don't you draw it?   Then, before posting it, consider carefully what the voltages will be under the various conditions. I suspect you'll find that there is a path with your idea that causes problems.
Copper is expensive?
The OP37 is also not unity-gain stable. From the datasheet: 
The OPA637 isn't unity-gain stable; the ground channel is unity gain. That's why they make the 627.
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...
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