I have a Commodore 1581 (800k 3.5" DD) floppy drive which reads and writes data just fine (with DD disks only of course), but it crashes (drive keeps spinning forever, stops moving the head and stops reacting to any commands) when you try to format a disk, e.g. with C64 BASIC commands such as OPEN 1,8,15,"N0:TEST DISK,TD". In the past I have used PC based tools such as 1581copy to do the formatting, but now that my last PC mainboard that supports non-USB floppy drives has died.

Is the formatting problem known? Is there any known fix?

Update: It freezes during the first few tracks, not always at the same place, but never manages to get more than about 10 (of 80) tracks done. I've tried formatting empty (factory sealed new old stock) disks, previously 1581 formatted disks, previously PC and Amiga formatted disks... no dice. If I use disks already formatted in 1581 format (either using 1581copy on the PC, or old disks that were formatted with the now-broken 1581 drive before it developed this problem), I can read and write all sectors without any problems. The problem appeared after the drive had been in storage for a couple of years in the early 2000s. Physical inspection of the PCB showed no visible problems like corrosion, popped electrolytics etc.

  • Does it freeze immediately or after a while, is it always at the same track/same amount of time passing?
    – user6576
    Jun 23, 2021 at 13:16
  • Have you already tried RE-formatting a known-good disk?
    – Brian H
    Jun 23, 2021 at 13:39
  • I've updated the question with answers to your questions.
    – TeaRex
    Jun 24, 2021 at 11:12
  • Perhaps a problem with the index pulse, or perhaps the disk in or write protect switches are dirty. Do you have a multimeter or oscilloscope? Jun 24, 2021 at 16:46

1 Answer 1


first check the the voltages and ripple also during the format. then also test it during other longer write operations that involve a lot of head movements (and as such draw more power than any other activity). also check the clock generation and /reset lines, and make sure any and all sensors on the drive mechanics are clear of dust. the diskdrive psu's are subject to all the same defects other old psu's are and as such should be the first suspect.


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