It is from the mid-1980s motor Jay Electronics driver board (hopefully) undergoing resurrection. Of three capacitance meters here, only one will make a stab at it in-circuit, where it reads ~600nF ...

“Am I the first person to discover this?” is a tricky question when it comes to classic Macs, some of the most pored-over devices on the planet. But there’s a lot to suggest that user paul.gaastra, on ...