The ARP Quartet is not a real ARP. It was made and sold in Italy by SIEL as the SIEL Orchestra, and then ARP bought the rights to distribute in the US and rebranded it as the Quartet. It is a string synth with four sections of which two can be selected at a time, which are stacked, not split into two regions of the keyboard as is the case with some string synths.
Being “not a real ARP,” it does not have all the pitfalls that ARPs have: tantalum capacitors, crappy prototype-style PCBs, etc. It is the first synth I have ever worked on in which every IC is socketed! That’s amazing. I give it big points for that.
Service Tips: this has the kind of keyboard where the key contacts are made out of springy things like wound guitar strings (without a core though). Do not put DeOxit on these contacts. I’m not sure why, but they hate DeOxit. It doesn’t damage them, but it makes them work less well. It is much better to clean them with acetone. For the buss bar, I polish off the tarnish with regular household metal polish cream.
This one had a bad TDA1008 divider IC in a failure state in which all keys of that note played all octaves of the note– I hadn’t seen a TDA1008 do that before.
Work done: full replacement of all electrolytic capacitors (130+ capacitors!). Cleaned buss bar and key contacts, cleaned sliders and switches and lubricated sliders. Replaced one diode to fix envelope problem with one note, and one TDA1008 (discussed above).