Yamaha PSS-680 Repair

I recently acquired a Yahama PSS-680 keyboard in excellent condition from eBay. It mostly works fine, apart from a scratchy volume control slider and some of the effects buttons not operating.

It's quite nicely put together. It comes apart easily enough with some screws.

Looking inside, it's a dual layer PCB with some DIP packages on the underside (sorry about the quality of this photo).

On the top, it's all through-hole. There are some weird overlaid tracks (the blue ones). These seems to be an extra layer on top of the PCB tracks.

The issue was that the bottom five effects buttons don't work. I had a quick look and found what looked like a break in one of these overlaid tracks (centre of this photo, to the right of and between the third and fourth from the top lit LEDs). I verified that it was a break with a continuity test.

I tried to scrape away the blue layer to solder in a wire to mend the break, but it wasn't easy. I don't know if the traces are thinner than the main board ones. In the end I found a couple of pieces of track either side of the break on the main board, scraped off the solder mask with a knife, and soldered a piece of enamelled wire across. It's not pretty but it works.

It's proved reliable so far and everything works on the keyboard now.