PC diskette drives in a HP 9122C was WTB: HP-85 16k RAM Module and HPIB Floppy Drive

Paul Berger phb.hfx at gmail.com
Thu Nov 23 21:02:29 CST 2017

I have managed to get 2 PC type drives working in a 9122C they are two 
different versions of the YE Data YD-702D.  The important thing is the 
drive needs to provide a ready signal, diskette change and density.  
Most drives provide the last two but do not have a ready signal.  You 
also need to leave pin 1 unconnected this is a signal from the 
controller to reset the diskette changed signal.  One of the drive the 
YD-702D-6037 can also be altered by moving jumpers to get power from the 
cable.  The other a YD-702D-6537D does not and it unfortunately seems to 
be the more common drive.  I changed the drives so that ready is on Pin 
34, diskette change on pin 2 and density on pin 4, the same as the Sony 
drive in the 9122C.  I did encounter one problem where if I tried to CAT 
a diskette it would always report that the diskette was changed or 
missing and I recall encountering this previously, it may be related to 
how the diskette changed signal gets reset. On most "standard" 3.5" 
drives the diskette changed signal gets reset as soon as the drive is 
selected and receives a step pulse. On the Sony drives used in the 9122C 
reset the diskette changed signal by a pulse on pin 1 from the 
controller.  What I think is happening is when media is changed, the 
controller thinks it does not have to move the head so the diskette 
changed never gets reset so the controller continues to think the 
diskette has been changed, I will do more testing to verify.  I thought 
that booting with the drive empty provoked this but that is not the 
case.  I can post details of the modifications to the drives if anyone 
is interested.


On 2017-11-17 1:26 PM, Paul Berger wrote:
> I just checked my 9122C I happen to have open and the interval between 
> index pulses is 199.66mS  which would be 300 RPM, which is good news 
> for me I can now proceed with adapting a more common 1.44 drive to 
> replace my broken one.
> Paul.
> On 2017-11-17 1:04 PM, Eric Schlaepfer via cctalk wrote:
>> Check your email. How can you tell if it uses a 600 RPM mechanism or 
>> not?
>> On Thu, Nov 16, 2017 at 3:17 AM, Eric Smith <spacewar at gmail.com> wrote:
>>> Hi Eric,
>>> It's not urgent, but when you have a chance, could you dump the 9122C
>>> ROM(s) and take high resolution photos of the controller board?
>>> Since it does HD, I suspect it probably does not use a 600 RPM 
>>> mechanism.
>>> Thanks!
>>> Best regards,
>>> Eric

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