Apple IIC floppy drive can read.. but not write floppy

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Last seen: 2 years 8 months ago
Joined: Mar 10 2021 - 16:00
Posts: 1
Apple IIC floppy drive can read.. but not write floppy

Hi, I have a very strange problem with an Apple IIC.  (To better understand the issue I attached 3 videos)

Initially I suspected the problem was the drive, so I bought a new one but got the same behavior (Heads cleaned on each one).

I can read, but not write or format floppy (by using ADTPRO). I also tried to load DOS using ADTPRO and execute the command INIT HELLO, without no success.

When i try to format a floppy, the head is moving to all surface, but at the end I get always "Check disk or drive door" (See VIDEO 2 FORMAT) if i using ADTPRO, while using the DOS loaded using ADTPRO i get the I/O error instantly (the head do not move).

Testing signals on the IWM all seems ok but when I'm trying to write an image using ADTPRO, with an oscilloscope I checked that the WRDATA PIN remain HIGH, while the WRREQ pin remain LOW (I supposed to see pulses on the WRDATA pin) and the floppy head remain fixed, so this is because the floppy is not formatted right?  (See VIDEO 1 WRITE AN IMAGE)

I also bypassed the Write Protect circuit of one drive (suspecting something regarding this) installing a socket for the 74LS125IC, disconnecting the pin 3 of the 74LS125IC from the socket and keeping the pin on the socket down to ground, but nothing change. The Write Protect circuit seems ok even before doing this modification on a drive (if I try to format a protected floppy the format process whas stopped instantly while if i use a not protected floppy the heads move, like in the VIDEO 3 FORMAT)


I tried different floppys, but nothing change. I don't suspect about the heads or head moving mechanism, just because i can read floppy (see VIDEO 3 READ)


Thanks in advance







Last seen: 2 years 7 months ago
Joined: Apr 3 2021 - 12:07
Posts: 1

I had a similar issue on one my IIcs, and it turned out to be the disk drive speed.  Running diagnostics showed that it was running too far.  Non-copy protected disks would load, but not write.

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