CDC 9429 Floppy maintenance manual

Fred Cisin cisin at
Sun May 8 15:09:06 CDT 2016

>>> I have reason to believe that the CDC 9428 and 9429 are identical
>>> except that the 9429 is jumpered for 80 tracks and the 9428 is
>>> jumpered for 40 tracks... but I'm not 100% sure.
> * On Sat, May 07, 2016 at 11:17:50PM -0600, Eric Smith <spacewar at> wrote:
>> They would have to have different heads, if the 40 track model was
>> standards-compliant and industry-compatible.

On Sun, 8 May 2016, Seth Morabito wrote:
> Ahhh... of course, I should have thought of that.
> I am even more cautious about using the 9428 manual for 9429
> service, then.

Actually, many lines of drives, such as the Tandon TM100 have the same 
circuitry for both the 48tpi and 96tpi variants. (and the TM100-4M at 

A specific exception, that I don't think is relevant here, is that a 1.2M 
drive will have a few circuitry changes V a 48tpi/"360K" model, such as 
RWC (reduced write current), and sometimes a 300RPM V 360RPM control.

But, a "360K" (CDC 9428) V "720K" (CDC 9429) are likely to be virtually 
identical other than step distance and head width.

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