Oct 1 2016
A friend asked me if I would help fix her digital piano. I assured her that I would love to. Her and her husband delivered it to me in the evening and told me that the volume control (a sliding potentiometer) stopped working.
Knowing the general quality of Yamaha products, I went for it. After the kids went to bed, I dove in and started removing screws. It quickly became apparent that nearly all of the screws on the back would need to come out. Thankfully, all of the 83! screws were identical and came out quickly.
[img of screw piles]
The main body of the piano separated into two pieces after removing the screws. I needed to remove another round of screws (luckily fewer this time) to extract the array of keys.
[image of keys]
Finally I got at the heart of the problem, the non-functional sliding potentiometer. I spent a while googling replacements which were hard to find or cost 30$ and would take weeks to ship. I also spent a while examining the traces on the board it was soldered to in an effort to understand what the various pins were supposed to do. I found the specs for this pot online and it was measuring pretty much broken. At some point I figured, this thing is already broken and needs replacing; I’ll just pry it apart and see what’s wrong. It’s not meant to be taken apart, but that didn’t stop me.
[image of broken pot]
Lo and behold it was that the super tiny pieces of metal that drag along the potentiometer surface were fairly mangled. With some careful tweezering, I bent them back into shape and was able to re-assemble the pot (after several tries). I plugged in the piano while it was disassembled and it worked! It took a bit to re-assemble the hundred or so screws, but it went pretty smoothly.
I gave the piano back to my friend the next morning and she was very happy. It had been two years since it worked and several repair shops had turned them away.
[image of re-assembled piano]