Low leakage cap for synth CV

[NoisyIndividual]

It's difficult to take a time machine and test an SH strait from factory but I won't say crap !
To summary, probably the FET is faulty if without him you get aprox 30 sec for a semitone detune ?
But 30 sec is still short (depending of music you want to perform), so if you have already everything opened and pcb out you'll have to float that node

I suspect the replacement of the FET will restore it to near factory conditions.

Upgrading it is a whole new ball game.

 

[AnalogPackrat]

I suspect the replacement of the FET will restore it to near factory conditions.

Upgrading it is a whole new ball game.

If you've pulled the hold cap and the FET, why not desolder the op-amp input pin so you can float the cap node off-board? You're 2/3 of the way there already.