Hi I have a Roland U-20 from 1988, I was curious as to what could cause the polyphonic aftertouch to not function, other than that the synth works good, and it is one of my favorites in my synth corner
The problem could be that the aftertouch contact strip is dirty from oxidation. It’s tricky to clean because they glue it down.
The other possible problem could be Roland poor implementation of Aftertouch. The link below talks about a mod for the aftertouch on a U20. It sounds like the same problem as you find on most A-80. Poor to non existence aftertouch
http://llamamusic.com/u20/u-20_info.html#aftertouch
Hope this helps