I've got a later version of the keyboard as the double strip does not seam to be brass but probably conductive carbon. I gave it a clean with isopropyl alcohol (IPA). That is probably all I can do with this. As far as the other component (felt strip side) it looks like a brass strip with conductive rubber. I've cleaned that too with IPA.
I suspect the problem lies with the conductive rubber on the top metal strip. After 35 years it probably loses its conductive properties. Maybe upping the gain on the AT circuit would be the best bet. I'm not sure if I want to go that far however.
Have been researching the net a bit and for tough cases of key not working you could use conductive paint, which is recommended by some polysix users who rubbed off the conductive layer of their key contacts. Not sure this will work for the aftertouch though.
The two black strips on the PCB need a gentle clean with Isoprop alcohol... as pure as you can get... clean gently so the black becomes a graphite grey with a slight sheen to it. Keep cleaning beyond this and you will remove all the conductive stuff off the bottom strip... your Q‑Tip or cotton bud will still look like there is dirt on it whilst you clean EVERYTHING off.... just work on a few inches at a time so you can see the difference. In the past I have used the conductive PCB repair pens to restore breaks or bits that people have cleaned off.... ONLY apply to the lower strips attached to the keybed PCB... and do not apply over the top of an uncleaned PCB strip.
Some of you are wondering about my after touch endeavors. That did not go as hoped. My initial goal was keep it simple and perform a cleaning exercise of all the AT components. I cleaned the bottom two graphite strips with IPA (be gentle as the graphite will easily rub off). I cleaned the top pressure strip (conductive foam & brass strip) with IPA as well. Note that the pressure sensitive foam (or rubber) is permanently adhered to the brass strip. It can not be removed. i simply cleaned the exposed side of the foam. Now when i put it all together i have to say i did get a response from the AT but with quite some force required. Not ideal when playing. The root of the problem is the conductive foam (rubber). This needs to be replaced.
Zoflex produces a Pressure Sensitive Conductive Rubber Sheet. I'm wondering if this can be used to replace the original foam. I do not have immediate plans to try it but i think i will at some point when time permits. Some of you with a more electrical background may want to comment on the feasibility of this product. just a thought...
This Zoflex a good find! I think it has possibilities. The price is not too bad for the area it can cover and also... considering that you can't buy replacement parts anywhere, I think it's worth a try.
The aftertouch strips are made from a carbon compound and need a clean with Isopropyl Alcohol and some Q‑Tips...gently clean half an octave at a time and you will see the black strips turn to a dark grey with a slight lustre to them..STOP THERE..or you could clean the conductive stuff right off.....As for the top strip, give it a wipe over with a cloth dampened with Isopropyl and then wipe off with a clean cloth....the top strip is not so critical to clean....As for the felt try googling for piano repairs locally as its the same stuff that goes under piano keys/hammer return stops.
Many thanks for the advice. I've reached out to a couple of piano repair guys and hopefully will get a response regarding the felt. A few knowledgeable gents on the Analogue Heaven mailing list also suggested I try pool table installation & service companies, which seems like a fab idea.
Update: After having a look at pool table felt and deciding against it (far too thin and hard for this application), I found a local, independent piano repairman who sold me some perfectly sized felt strips for $5.
Regarding the aftertouch strip - many accounts I've read online suggest removing the (extremely thin) black rubber strip you can see on the upper portion of the strip (right side of the photo) so as to clean the foil beneath it. You feel that this is unnecessary? I tried gently prying it up last night and it did not want budge . . . so I'd be happy to not tamper with it if I don't have to.
No leave that black mesh in place. 99.9% of the problem is the lower strip oxidizing...simply wiping the top strip with moist then dry cloth will flex the rubber mesh and get the job done without destroying the top strip
After cleaning the two carbon strips with isopropyl, and giving the rubber mesh on the top strip an ISO wipe, I reassembled the keybed and found that while functional, the aftertouch still required way too much pressure to activate - more than I'd ever be able to apply naturally while playing. So I decided to give the graphite powder a shot. I rubbed new graphite powder (purchased for under $5 at my local hardware store) onto the carbon strips with a Q‑Tip and reassembled again. This time the aftertouch effect was too strong. Even with the Aftertouch Sensitivity slider up only a smidgen there was Aftertouch Mod very much audible with the least amount of key pressure. So I disassembled again and wiped off all the graphite powder I could with a clean cloth and a bit of isopropyl. I reassembled, and Shazam! - perfect aftertouch response. Seriously, it's exactly as responsive now as I'd expect/want it to be if the board was brand new from the factory. How long it will last I have no idea.
So I don't know if there's a faster way, but I got what I was after by following this procedure:
1. Remove upper portion of aftertouch strip and clean lower carbon strip pair with a Q‑Tip and Isopropyl. Rub lightly until the black strips become dark grey like the lead in a pencil - don't overdo it or you might damage the strips!
2. Give the black rubber strip on the top (removed portion) of the aftertouch strip assembly a wipe with a clean cloth and some isopropyl.
3. Rub graphite powder onto the lower carbon strip pair with a Q‑Tip.
4. Remove all traces of excess graphite powder by wiping the carbon strips with clean cloth and a bit of isopropyl.
5. Reassemble and enjoy!