Vintage Synth Repair

> Now when one releases the key, it hangs and tends to lift up by a semitone or
> so.

This is not uncommon. I don't know offhand if this could be a calibration
issue (probably not). However I have observed that the whole CV memory
circuit is very sensitive to dust, dirt and other contamination. A very
thorough cleaning of this area might already do the job; in addition I tend
to exchange the opamps if there is even a slight problem.

On to the next issue:

> If I set the output to the main VCA - AR - it will remain audible endlessly.
> If I set it to ADSR, it can fade away (though I believe the signal is still
> passing though up to that envelope. The ADSR just happens to hide the signal
> by fading it out).

I'm not sure if I follow you completely: Of course the signal will pass up
to the envelope (or more correctly: to the VCA). There will always be
signal in front of the VCA, regardless if a key is pressed or not! (Ok, it
depends on several other factors as well; but with a basic patch you will
get signal.)

At this point I would start by verifying if the ADSR is working properly
and is triggered/gated properly. This is easiest performed with either the
VCO or the VCF (due to the still persisting CV problem I'd suggest the VCF
route):

Set all four ADSR sliders to about 50%.
Send noise into VCF.
Set VCF Freq and resonance to roughly 50%.
Set ADSR to VCF to 100%% (and of course the switch to ADSR.
Set VCA Gain to 100%.
Set VCA ADSR/AR slider to zero.

Observe results. You should get a constant smooth noise. Now press a key.
If the ADSR works the noise should get brighter, then slightly darker (and
should stay this way as long as you hold the key), and then get darker
again after you release the key.