NEC Drive Problem (CP/M System)

From: Bill Yakowenko <>
Date: Fri Sep 19 23:11:51 2003

Sounds like a "seek" problem to me. If it uses the old Western Digital
floppy controller, you could issue seek instructions pretty easily to
test that. I suppose other controllers might be similar. I'd have to
hit the WD databook for details, but it was something like writing a
track number into one register, then writing the "seek" command into
another, then sitting back and enjoying the whir-click sound of a seek.
Then a "restore" command would get it back to track 0. I've done it
on TRS-80's; not sure if it would be quite so easy under CP/M.

Cautionary note though: the OS probably remembers what track it last
positioned the drive to, and may be confused if you leave it at a
different track. I *think* any attempted read/write would then fail
with a "no such sector found" error, after which the OS would probably
just automatically re-seek & re-try, resulting in no problem. But I
wouldn't bet my last bootable floppy on it.

I've seen a seek mechanism stuck - refused to move until I powered
the thing down, opened it up, & physically slid the head back and forth
along the rails a few times. After which it worked. YMMV, of course.

One other possibility, I've seen (somewhere) a disk format in which
track 0 was always written in single density for compatibility with
older drives, while the rest of the disk could be SD or DD. So an
older system could give the appropriate error message when failing to
read a DD disk (more specific than just "unreadable"). Was that CP/M?
If so, then the problem could be a failure in handling DD data.

And it seems to me CP/M used "$$$" as some kind of temporary file
extension, renaming files to their proper extension at the end of the
operation...? Which would indicate again that the track-0 commands
succeeded, but the other-track commands failed, leaving the disk op


> From: "Mike Davis" <>
> To:
> Date: Thu, 18 Sep 2003 08:43:53 -0700
> Subject: NEC Drive Problem (CP/M System)
> Reply-To:
> Ok, I have a puzzle that I need help on. I have an NEC Dual 8"
> Drive System. This is a CP/M system. But my drive #2 has a problem.
> Drive #1 works fine.
> Symptoms:
> Can't boot from drive #2
> Can't read files from drive #2
> Can't write files to drive #2
> CAN get a directory listing from drive #2
> CAN write to FAT, as when trying to copy files
> If I try to load files from drive #2, I get a failure with the
> following error: "Bdos Err On B: Bad Sector"
> If I try to write files to drive #2, the directory entry is written
> (except that it is TEST.$$$ instead of the correct extension). But
> the data for the file is apparently NOT written. I get the same
> error.
> I see attempts to read and write but these always end with the error
> above.
> It looks like the write head must be good, as a filename is saved to
> disk. It looks like the read head must be good, as the directory can
> be listed.
> Any suggestions as to what could be causing this? Could it have
> something with head movement? Perhaps the directory storage is on a
> track (sector) that can be reached and the others can't? I'm stumped.
> Note: I have not actually looked inside to see if the head is moving
> properly (that may be next but I know it does move some.) but I have
> reattached all the connectors to the drive and controller.
> The drive is an FD1165-A. I can't locate such a drive. But I have
> located an FD1165-FQ. I wonder how compatible the FQ version is with
> the A version. Can parts be exchanged?
Received on Fri Sep 19 2003 - 23:11:51 BST

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