It suggests that the "fragile" part is a
6530 - a part made by
Commodore that was always customized for its particular application.
I've seen them on the KIM-1, in many Commodore disk drives and a
few other places. Apparently some drives (perhaps the DOS 3.0 ones)
used a daughter card in the 6530 socket with a 6532 (which is generic)
and an external ROM.
Mine has that, but I thought the chips on the daughtercard were a 6530
(from which the ROM section is not used, so any 6530 should work), and a
ROM. Oh, and maybe a bit of glue logic.
Dunno what's wrong with your father's drive, but if you can get in
front of it, turn it on and watch for flashing lights. In many cases,
If the lights keep on flashing when you power up, count the number of
flashes between pauses. Then post that number. I think it's the same for
the 8050, for which I have the official service manual...
-tony