Boss DD3 Repair Mystery - Signal not passing IC

[clarisso11]

Signal at pin2 is extremely low as this is a virtual earth node by the inverting opamp configuration.

You should be able to scope the dry signal before R13. If you see signal there check R13 and/or look for a broken board trace.

Thank you, that explains why I couldn't get a signal on the scope. I was able to confirm dry signal before R13 on the broken unit, it is identical to the one on the working unit.

[clarisso11]

You say you can hear amplification between pins 2 and 1 for both units, but scope does not confirm this. Wet signal can still bleed around IC1a via R16.
Is E.Level pot working when you hear only wet? You should be able to kill the wet signal with the E.level pot.
We used to get some of these where the jacks got swapped around or mis-wired. Double check against your good unit just to be sure.

Thanks, I never thought of that! I checked and the wiring looks identical, so at least that's ruled out.

[clarisso11]

You can't go by the DC drain and source voltages as they are both sitting around 1/2 VCC at all times (unless defective IC1).
Agree that shorting drain to source easier than swapping with Q8.

Looks like Q5 was the culprit! I shorted drain to source as suggested, and it restored the dry signal at IC1 pin1.

In stereo mode (when something plugged into direct out), mono out becomes wet only. This is achieved by turning off Q5. If Q5 off, then also no signal in bypass mode

This seems to be exactly what was going on - I can't believe I spent hours hunting down a loose connection. Will try replacing Q5 with 2n5457.

Thanks everyone for your help, I think we're back in business!

[clarisso11]

Just a quick note: 2n5457 didn't do the trick, but I had a 2SK30A lying around that works well.