Epson PX-8 specifically TF-10 problem...

allison allisonportable at
Sat Dec 9 20:06:58 CST 2017

On 12/09/2017 07:52 PM, Fred Cisin via cctalk wrote:
> On Sat, 9 Dec 2017, allison via cctalk wrote:
>> I have several Epson PX-8s and i used them.. They work well with the
>> various wedges I have.
>> I also Have a PF-10 which is the portable 3.5" 40 track two side floppy.
>> The problem is it randomly does not turn the media unless I give it a
>> push to get it turning.
>> Things checked:
>> * Batteries, NEW fully charge (Both).
>> * internal Power supplies, current voltage and bridged with external
>>    supplies does not help.
>> * media checked for binding, it does not.
>>  When it turns it reads and writes correctly and at the correct speed.
>>  It may do so without help for many tries then will stop required a
>> manual push.
>> At first glance I though there were motor bearing issues but have
>> verified
>> this is not so.   If I force motor on and restrain it I has good torque
>> and no
>> dead spots.  All signals in the motor control look good on the scope.
>> Any thoughts?
> How does it detect the presence of a disk?   and/or disk change?
Functions normally save for the motor does not always turn on command
but will if manually pushed.  All other functions are normal.

> Totally irrelevant to the matter at hand:
> BTW, how close to "industry standard" is the interface to the drive
> mechanism itself?   Would it be practical to replace the mechanism
> with one of the 80 track (and also 2 sided?) Epson drives?  Either the
> whole drive, if it is fairly "standard", or just the stepping
> mechanism if there is another Epson drive similar enough?

No its an oddball.  The read-wirite electronics are part of the
intelligent mainboard that communicates
with the pX-8 serially.  The only board that is part of the drive is the
motor control.

Its of the early 80s.   It would be nice to build a replacement with
more storage but the basic design
is a 68B03, 2732 and 765 with read/write amps and filter on that
board.    It would be easier to start
from scratch with an 8085 and a 37c65 but then that would require
figuring out the protocol and
patching the OS (CP/M-80 in Eprom) to accept the larger result.  If I
were to do that I'd do a solidstate
disk using CF or SD.  Its easier to do that using the PX-8 system bus
(parallel data, address and Z80 controls).

> Besides significant increase in capacity, it would simplify data
> interchange a bit.
> Although the track spacing is 67.5 tpi, instead of 135tpi, I wonder
> whether the track width is similarly different.

Its not unlike the 5.25" situation with track width as in the the higher
density drives
have narrower heads.  Not unlike Sa450 and FD33GFR.  I can read the
media with
a standard drive by double stepping but to create media I have to first
erase and then write only every other track or it has a poor error rate.


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