• Updated 2023-07-12: Hello, Guest! Welcome back, and be sure to check out this follow-up post about our outage a week or so ago.

My first Apple computer, a Mac IIcx


Well-known member
UM5 - looks like an Apple specific clock IC
UM5 is the Apple 'Real Time Clock' (RTC) chip. Looks like yours may still be OK - as long as the legs are not completely corroded away, they may just need some cleanup with vinegar and possibly sanded a bit to bring them back.

Y4 - presumably a crystal for the clock
Y4 a crystal, its on page 4 of the Bomarc schematics.


F3 - a fuse?

F3 is a fuse, it's for the internal/external floppy I/O. F1 and F2 are on the Bomarc schematics as SMD200 2A.