One of the IC's had a hole in it. Looked like it
burned out.
He said it was the first time he's ever seen that!
The Apple II floppy drives were notorious for this. The chip
that drove the stepper motor (I forget the part number) would
literally explode, leaving a quite visible crater in the top
of the IC.
It got to the point where, as a customer walked into the shop with
a broken drive, I could diagnose the problem from across the room
because those exploded chips emitted a unique odor.
We made a fair bit of cash swapping those ICs :-)
--lyndon