Elka Twin 61 - Section A: failed C2 key and failed D octave

Synth Repair
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[Elka] [Elkatwin-61] – [D octave fail and C2 key fail (both in Section A)]

I have an Elkatwin 61 that has been in storage for many years. I start it up with its swell pedal connected and everything is OK except for a dead D octave (all the D keys are mute) in section A and the C2 key (lowest C after the Bass section) is also mute.

The B section plays those keys fine, as does the Bass section.

Chat GPT has got me far enough to know that this is likely either

A: A contact / wiring issue that is probably an easy fix (deox / soldering a cold solder) or
B: A sub-oscillator chip issue requiring a replacement (beyond my skills) - however I would at least like to rule out a quick fix and was hoping someone could point me to where a possible connection fault might lie to rule out A.

I have the Schematics but my electronic skills are limited to soldering guitar cables. I was hoping someone could identify where in the synth I should be looking for a cold solder or broken cable: https://www.vintagesynthparts.com/wp-content/uploads/2018/01/ElkaTwin61_Schematics_1981.pdf

I am in Norway so I’m afraid it would be quite prohibitive to send the synth overseas for repair. Theres a great pro here in Oslo but I think the going rate for synth repair is over 120 dollars an hour here and I would be terrified of a gigantic bill for a synth that sadly is likely not worth that kind of expense… I would just love to hear it working again.

Thanks for your attention.
H

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You can only inspect the area and check continuity between chips. Is there any corrosion?

The circuit diagram is hard to read as it’s quite old and hand drawn.

If the bad keys meet at a certain functional part, then that’s a good place to start.

Chips can usually be found online at Aliexpress if you struggle to find them locally.

Sorry I can’t be any more helpful, but persevere and I hope you find the solution.

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Thanks Sargfowler - no the insides look pristine with no visible corrosion that I can see. I am looking ofr blue stains at the ends of caps etc - but nothing. I have not yet started disassembling - or even pulling out cable plugs. I want to be more confident of what I’m doing. I understand things can be quite brittle after 50 years, and i don’t really want to create more problems yet.

I am hoping this is a small enough issue that it can be easily (and cheaply) fixed by a pro… rather than require a massive operation and refit…