CDC 9429 Floppy maintenance manual

Fred Cisin cisin at
Sun May 8 16:18:04 CDT 2016

>> Oddly, my own troubles with the SA-400 (believe it or not, this was used
>> as the original IBM offering for the 5150 drive) were with the tach
>> circuit.  Mine blew a small inductor.

On Sun, 8 May 2016, Paul Berger wrote:
> Are you sure about the SA-400 being used in 5150s?  All the ones I ever saw 
> where Tandon TM-100s which look very much like them and I saw lots as a 
> support person in an IBM lab in the early 80s.  They have the same sort of 
> motor setup to turn the diskette, but use a different head positioner.   The 
> TM-100s used a stepper with a taut band positioner.

The first 5150s that I had, or saw, had Tandon TM100-1 (single sided).
Followed (along with PC-DOS 1.10) with the TM100-2 (double sided).  Later, 
I started to see some other brands of drives used by IBM in 5150s, but 
NEVER Shugart SA400.
It would have at least had to be the SA400-L, since the SA400 was 35 
track, and PC-DOS, from the get-go, used 40 tracks.

The SA400 was, however, the original offering for the TRS80.  Followed 
later by TM100-1 and a few others.

And the SA390 (same mechanism, but without the circuit board) was used as 
original offering for Apple.  There was an unconfirmed rumor that, for a 
while, when they ran short, that Apple bought SA400s and removed the 

I agree about Micropolis; it was the most reliable drive that I had, 
although kinda slow stepping.

The LEAST reliable drives that I tried were the BASF 2/3 height, followed 
by the Qumetrak 142 (early 1/2 height)

Worst problem that we faced with the TM100s was that students in the 
computer labs would let the door slam when opening, breaking the hinge.

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