Hi there,
I recently bought an A500 second hand. When I got it, some of the keys on the keyboard weren't working (maybe half of the keys).
When I opened it up, I saw that the previous owner had probably tried to fix it by appling graphite (or something similar) to the keyboard connector cable:

I reckoned it needed a clean up, as there seemed to be some bridging between the tracks. After a round of nail polish and a q-tip it looked like this:

After that only one key was working (left bracket key).
I ordered a silver pen for circuit boards on eBay, hoping to retrace the tracks - do you guys think that's a feasible fix or a waste of time?
Thanks!
Hi, you may find a replacement membrane or keyboard here:
http://stores.ebay.com/Amiga-Retro-Experience/Amiga-500-Parts-/_i.html?_fsub=7That is the carbon conductive coating that has come off - not good. Non-repairable. I been there. No worky, worky for repair.

Best to find a good replacement assembly or membrane. If you replace just the membrane, make sure you get the right part number. Hope this helps.
Cheers!!
John