Howdy Kev.......D2 didn't have any limiting resistor when the tip saw +9
vdc so probably blew. It doesn't protect as much as limit the "on"
current of TS2 and TS4 (the affected stages). Putting +9 vdc to the
ring shouldn't have hurt the non-inverting input of that op amp in A6
via the pot and putting +9 vdc to the sleeve was just a short of itself.
With D2 blown, if open, TS2 and 4 will be turned on all the time and may
be warm (depending on their specs). You should be able to reverse their
switching (test them) by merely grounding the ring terminal of the
remote jack OR by activating SW2.

What doesn't work as it stands now?

Gord