Today I got this! A 1980s Yamaha PSR-12.
£2 from the local charity shop owner( he puts aside synthy stuff for me
) I thought it would be good to have another instrument to play on top of Kosmo. Looking online the sounds seem to come from an FM synth chip, and there’s a few quite invasive circuit bends that I probably won’t attempt ( 50/50 past success rate 
).Some of the bell sounds are a bit cheesy, but it has some good drum patterns and will probably come in quite handy.
Edit: I also found a service manual for the PSR-11 that seems to have the same functions. It has a most excellent exploded diagram that I might just have to print out and stick on the wall.
Edit edit: YAMAHA PSR11 Service Manual download, schematics, eeprom, repair info for electronics experts