Tried a new keyboard repair
I had ordered a keyboard repair set for keyboards using the "rubber membrane with carbon peg against PCB traces"-style contacts.
These are used on many keyboards such as the Juno-2, JX-8P, Polysix and of course Poly-61.
Cleaning the PCB and the carbon only seems to remove the very worst of the grease and dust but I didn't get a feeling that the keyboard was really "like new" in terms of triggering afterwards.
So, I decided to try these things...
You can see how thin they are. They come pre-punched with an adhesive so you peel them off of the tape, like little stickers.
I ordered them from sounddoctorin.com and decided to potentially sacrifice my Poly-61 by letting it be my guinea-pig.
I removed the keyboard from the Poly-61 and, while watching some football on TV, I used a small X-Acto knife to remove them from the strip and place them on the old carbon disc. After placing the disc I put the side of the knife against it and pressed with my thumb to make sure it would stick.
Here's a photo of one keyboard contact strip. All the contacts on this one has the new disc already attached, except the one on the left.
They're just a liiiittle bigger than the original and it's hard to get them perfectly centered but as long as they're covering the old one completely it should be good enough.
Of course, if you haven't cleaned your key contacts first you should do it but since I had cleaned mine again not long ago I didn't really bother.
After placing all 61 of them (I lost one because it wanted to become airborne), which took me about an hour and a half while watching TV at the same time, I reassembled they Poly-61 and tried it.
To my disappointment the top C and one of the other keys did not respond. I wiggled them a bit and hit them hard a few times, and then they worked. Maybe the rubber membrane hadn't come up through the hole completely or.. I don't know...Something else..
Anyway, it was working perfectly afterwards. All keys are responding "like new" (really) and it was a joy to actually play it now :)
I just have a small feeling that they trigger a tad early now, due to the extra height added to the contact, but maybe that is just my expectations causing me to suspect that. I didn't really compare between before and after. Now they trigger about half-way down. Maybe that's normal. I don't know. Either way it's better to trigger half-way down than every 3rd time or not at all :)
All that remains now is to see how long this lasts and if they fall off...
Anyway, highly recommended for anyone with similar problems!
I have enough of these for about 8 more keyboards (or 4 if they are velocity sensitive keys like Juno-2 and JX-8P due to having 2 contacts per key) and I'm definitely going to try them on the next keyboard I am having trouble with!