Vintage Synth Repair

Hi folks! 

I've been trying to pin down a problem with an Arp Omni MKI. It was in horrid condition when it arrived so I've gone a long way to recovering it. In a nutshell it's as the title suggests. Attack appears to work and so does Release, but having the note actually pressed cuts the sound out one Attack has done its job. It's only when I relese the key that 'release' is triggered. I hope that's a reasonably clear description.

I've started to follow the path as the manual suggests but I've reached a dead end. It refers to C15 switch from 0 to -15V when a key is pressed. This appears to be working. It referes to CR11 a bit fruther along and this also appears to work. Kind of lost my way from here.

Thanks in advance ~