Bridged Output Jack for ADA Microtube 100

[Enzo]

The ICs are cheap. But they are also CMOS, which means they are pretty sensitive, so I wouldn't be surprised the meter could trigger it. However, it suggests to me the circuit is open and pin 10 might be floating?

It looks to me like pin 10 ought to toggle between grounded with the jack empty, to -12v with something plugged into the jack (and thus opening the contacts). Does this occur reliably?

[allsignalmustpass]

It doesn't. jumping C3 and C4 (the isolated switch within the jack) does not reliably change the voltage.

[Enzo]

OK, then power off, resistance to ground from pin 10. Should toggle from open to short with jack action. I will wager it stays open? In that case, start with one probe on pin 10, and check for continuity - zero resistance - to C3 on the board with the other probe, then to C3 on the jack, then to C4 on the jack, then to C4 on the board, then to the ground. Find WHERE the continuity is lost.

You still could have a bad 4053, but ANY 4053 won't work if the control voltage doesn't get there.

Jumping C3,4 in the jack is one thing, but what happens if you jumper C3,4 on the board?

[allsignalmustpass]

It was the 4053! Thanks guys for all of your help! I put a new one in and socketed it in case anyone else has to work on it.