Crumar Stratus Restoration - VCF Issues

[Miracle_Nosh]

Hi all!

This is my first post here (I didn't realise this place existed until recently), and I hope you all don't mind that it's a request for help.

I'm in the middle of attempting to restore an old Crumar Stratus which was riddled with problems, and so far, it's been going well - but I've now hit a bit of a snag. Five of the six "articulation" (EG, VCF and VCA) boards play and respond just fine, but the VCF on the sixth board seems to be, for want of a better word, dead. It still passes audio for its two as assigned notes, and the ADSR aspect still works, but the VCF is having no effect on the sound; it just passes through unfiltered.

I've swapped the boards around, and can confirm that it's not the socket or motherboard, the fault is with this one particular articulation board. At this point, I figured that maybe the 3320 was dead, so I swapped it with a known good 3320; no effect. Swapped the op-amp, too, to no avail. I can't see any obvious component or trace damage in the board, either, and the board pins/sockets have all been cleaned with contact cleaner.

Does anyone here have any insight or experience with this synth? I know it's a bit weird and obscure, to say the least, but I'm hoping someone could perhaps help; I'd really appreciate it. Learning the secrets of the Stratus has been an experience!

Edit: Typo.