After giving up trying to find a replacement slide potentiometer that fits the Matrix-6, in combination with the awful condition of the small board the slider is mounted on, I found an old board for sale at http://www.syntaur.com/ .
They know how to charge for their parts but I figured it has been long enough without any other solution.
So, I ordered the volume board, took the old one out, installed the new one...
More problems?The thing wouldn't start! Again...
Completely dead. I started looking for problems.
I didn't see any activity at all on the databus of the CPU.
I tried reseating as many chips as I could and tried starting it again, and it worked...
There are some serious problems with the sockets or other connectors in that thing...
Anyway, it works, I had to run the calibration sequence after reseating the CEM3396's but then it worked fine.
No more crappy rotary pot hanging in wires on the outside.
All I need now is a small cap for the slider :)
Oh, and I still have two keys on the keyboard that don't respond.
I forgot about those (an incomplete repair I did a while ago) and got a bit surprised there were problems with the keyboard, but then I remembered.
Guess I should fix those sometime... in the future... :)