CBM 3040 (4040) disk drive repair: spindle speed out of control @iz8dwf

iz8dwf | CBM 3040 (4040) disk drive repair: spindle speed out of control @iz8dwf | Uploaded December 2018 | Updated October 2024, 56 minutes ago.
Commodore 3040 (actually factory upgraded to 4040 firmware in 1979), S/N 502953, repair. One Shugart SA-390 developed a fault in the spindle speed controller PCB. The only IC on that PCB turned out to be the culprit.
The SA-390 is the bare mechanic, stripped down of almost all electronics, of the well known SA-400 disk drive.
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