Classic analog with cross modulation and flexible routings. And...a non-linear taper pot that goes 1 full step the first half of the movement up or down and the rest of the octave in the next half! Reeeow! Very discrete circuitry for '77 Due probably to legalities with ARP some of the duophonic circuitry got re-baked I think in the later versions.
Tuning tips for non-SRM model might be helpful as well. I've seen several problems with the SRM. A bad resistor heating a transistor array in mine I recall, taking out vco1. I recall some problem with envelopes...ahh yeah I replaced a bunch of 4016's. Just get a bag of them and go to work if it's like mine was! (After doing some diagnostics to confirm that it might be those that is. They're cheap and fail prone it seems in these. )
Check digi-key for slider caps!Black - 401-1215-ND, White - 401-1216-ND, Grey - 401-1217-ND,Red - 401-1218-ND
I think I have nearly all if not all parts for these machines. There are some resistor networks that one might have to wire in discretely. The SSM2040 is available rarely on ebay etc. but here is a engineered SSM2040 replacement Module
Contact Sound Doctorin'