Re: IMSAI 8" floppy disk system manual/schematics?

On May 1, 2:07 am, bobar <boba...@xxxxxxxxxxxxx> wrote:
I got an IMSAI (turnkey system - no front panel) with a dual 8" floppy
drive system, also from IMSAI.
I have been able to fix the computer, but unable to get the drives to
work. The system came with CP/M
and quite a bit of other software so it would be great to get it

Does anyone have a manual or schematics for the disk system? I have a
basic description of the DIO
controller card, but no schematics. Also, I have nothing on the boards
in the disk chassis. The drives
are from Calcomp, model 142M.

Any simple way to verify the disk components are working?

Photos of the system can be seen on my web site at:



I have a number of IMSAI manuals available as listed on my Web site at
the link below. Good photocopies are available for a modest per page

...and my home page to ALL my S-100 manuals is at this link:

I also have manuals for many floppy drives, same deal.

Just as a general caution, to everyone who gets an S-100 computer and
asks for documentation. PLEASE PLEASE PLEASE take time to identify
every board by BRAND AND MODEL. Same with floppy drives.

For instance, this person apparently requests docs for the "DIO"
floppy controller card set. But the apparent photo of the system (hard
to say, the Web page has several IMSAI and other systems on it) shows
what I think is a PIO-II controller - hard to read the board's text.
Any given S-100 system one buys, can have almost any kind of boards in
it, wherever the chasis was "from" 20 or 30 years ago.

Another question was about a "simple way to verify the disk
components". The early floppy disk controllers for S-100, designed
before the single-chip Western Digital controller IC's were available,
are very DIFFICULT to restore. They often used passive components
(resistors and capacitors) to control critical timing: thirty years
later those components are way off-value and should be replaced.
Processor timing is critical too, these boards run the processor flat-
out and use wait states, etc. Or, they will run on their own
processor. Often there is a seperate manual, just on tests and
adjustments of these boards. Also, some of the floppy disk formatting
schemes are not "standard" to those available from the WD chip sets
(or any other floppy controller), so you can't read "their" disks
anywhere else. Oh, and they may only support HARD SECTORED disks for
that matter, depending on vintage.

I can't imagine repairing these without an oscilloscope, and some
carefully prepared diskettes. Of course you need the full manuals and
tech notes.

Good luck!

Herb Johnson

Herbert R. Johnson, New Jersey USA web site domain mirror
my email address: hjohnson AAT retrotechnology DOTT com
if no reply, try in a few days: herbjohnson ATT comcast DOTT net
"Herb's Stuff": old Mac, SGI, 8-inch floppy drives
S-100 IMSAI Altair computers, docs, by "Dr. S-100"


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