Marshall 3210 Mosfet head. Can't turn off the boost channel.

[bclemons]

Let me correct the prior reading, it was 0.03v on 4,6, and 11. When I hit footswitch, I get 0.76v on 4,6, and 11.

[J M Fahey]

Let me correct the prior reading, it was 0.03v on 4,6, and 11. When I hit footswitch, I get 0.76v on 4,6, and 11.

Ok, you "get 0.76v on 4,6, and 11." .......... and? .................................... does the drive channel now get muted or not?

If it does, it was a poor solder job and now you solved it.
If it does not then CA3046 is dead.

[bclemons]

It was too late to keep working on the amp without disturbing the kids. I'm about to go try it now.

[bclemons]

It's working correctly now. Thank you all very much. Now I just have to replace the pot and jack that I destroyed in the process.

[J M Fahey]

So it was the +15V_through_R10 not reaching pins 4/6/11 which are transistor bases and would switch said transistors ON/OFF , muting audio when ON .... which didn't happen of course.

Said bases, being a forward biased diode, would alternate between 0V (no muting) and roughly 0.7V (muting).

As you see, it was repaired not replacing a single part , in this case logically finding a broken connection (bad soldering) .

Congratulations