My guess is that it could be caused by a dry solder joint on the 100k resistor between pin 1 of U2 A, and pin 6 of U2 B, or, that 100k resistor might have gone high in value, or gone open-circuit, there could also be a partial-short to ground from pin 6 of U2 B, as Simon said, first thing I would do is de-solder one leg of that 100k resistor and measure it with a digital multimeter, if it checks out to be within tolerance then that will eliminate the resistor as being the cause, hope that helps.
That 10k B output pot could also be the cause of the low output when un-bypassed, sometimes the solder-lugs on pots can go a bit loose if too much heat is put on them when soldering to the lugs, this will cause an intermittent connection to the carbon track.
Last edited by DrNomis_44; 17-06-2021 at 01:00 PM.
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