10 Jun
2007
10 Jun
'07
4:22 p.m.
Tony, many thanks - the schematics/circuit diagrams appear to be 100%
relevant to my board. I can now start trying to figure out what I zapped.
It looks like the -50 and -30 suffixes are little more than cosmetic changes
or switch configurations. My FDD is also a half height.
I think the motor speed is referenced to the master clock on that PCB --
there's a seramic resonator or something IIRC. In which case, if the
resonator is the same frequency, the chips the same types, and the motor
still has 6 coils, it'll be a 600 rpm unit.
I don't know how common 9114Bs are, but that might be a source of a
replacement drive. Ditto 9153s, but IIRC at least one version of those
(9153C) has a 1.44M 300rpm drive, which is exactly what you don't want!
I was thinking about the Z0765A FDC and how to make it compatible with a
300rpm FDD. It seems that all that needs to be done (in theory) is to
reduce all the FDC clocks by half - the 8MHz clock to 4MHz and the Write
Clock to 500KHz. (NEC indicates this in their uPD 765A datasheet). Clearly
not as simple to execute as it sounds, but not beyond the realms of
possibility.
You will also have to fiddle with the VCO (and maybe any loop filters) in
the data separator.
It should be possible, unless there;s some evil software that complains
if an index pulse takes too long to appear (I could believe anything from
HP self-tests!).
-tony