I killed an old Yamaha toy keyboard. I was trying to retrofit a MIDI input to a PSS-100 by emulating the keyboard matrix. I had mapped everything out, it was all going well, then I decided to look for a place to pull 5V off the board. My probe slipped, I accidentally bridged two contacts on the power transistor, heard a click, and now nothing works. It’ll either be easily fixable by replacing some passive components, or I’ll have managed to kill the ICs. As the power supply is now putting out 0.5 V instead of 5 V, I have some hope that it’s a power supply issue.