[sdiy] saw core VCO tuning/scaling (Roland SH-2)

[Adam Inglis]

I realise this is probably a timeworn query - my apologies to the  
veterans.

I'm having some trouble with my SH-2 (dual VCO monosynth 1979):
I've had it up on the bench a couple of times to calibrate VCO 1. VCO  
2 comes up sweet.
I leave it on for an hour, follow the SM routine ("width", then  
"linearity" then footages) and think it sounds good, check it with a  
tuner, but after I put back in the rack it goes out (of tune but also  
scale width) after an hour - so I guess it is temperature related.

The key CVs are spot-on, and the supply voltages seem solid. VCO 2  
remains fine. Measuring the voltages after the CV summing op-amp  
gives equal values between octaves. From that point, I'm not sure  
what to look for with my ancient scope and my Fluke - it's current- 
dependant, is it not?
The expo converters are metal can uA726 - they both run quite warm to  
touch.

I've read Ian Fritz's and Magnus Danielson's info regarding these  
type of Electronotes-based VCOs, but if anyone can point me to some  
troubleshooting articles, that would be most appreciated,


regards
Adam Inglis