"Wot I dun", last Thursday's edition: I think I've found out why 8 consecutive keys on my late uncle's digital piano keyboard don't work. While following traces on one of they keyboard PCBs I brushed away what seemed like a bit of blue-green dirt, only to find a little gap in the track underneath. I think the "dirt" must have been a crystal of corroded copper! The 8 keys the trace connects to are the ones that don't work, so I may have found the problem. Now just need to solder a bit of wire on to fix it. (Not sure I'm even going to try just bridging the gap with solder because it's in an area with lots of very tiny tracks very close together and I can barely see the individual tracks without a loupe. But either side are sparser areas where I should be able to solder a wire without too much trouble.)

My aunt has lamented that she didn't know while my uncle was alive that it was something I'd be able to fix. I didn't even know while he was alive that there was something wrong with it that needed fixing - apparently he was good at playing tunes that avoided those particular keys.