29 Oct
2024
29 Oct
'24
12:16 p.m.
On Mon, Oct 28, 2024 at 6:45 PM Fred Cisin via cctalk
<cctalk(a)classiccmp.org> wrote:
2) motor speed is not as easy as increasing/decreasing
voltage.
On a belt driven drive, you might be able to change pulleys. Althoug, I
think that a "50Hz" pulley on a "60Hz" drive might give you the
change
from 300 RPM to 360RPM?, . . .
Some/many?/all? 8 inch drives use synchronous motors (8 inch drive power
connections were NOT standardized!) with one of their voltages being a
lowered voltage AC
I've never seen a 5.25" or smaller floppy drive with a mains
sychronous motor. _Most_ 8" drives, including all the ones I've worked
on, did use such motors but I've read an 8" drive service manual where
the spindle motor was an electronically-controlled DC motor running
off the 24V supply.
As an aside, Tektronix used normal 8" drives in some of their
machines, always fitted with 60Hz pulley sets. They produced a 115V
60Hz output in the power supply, frequency contolled by a crystal. As
a result said machine would run off 50Hz mains, 60Hz and indeed 400Hz
aircraft supplies without pulley changes
3) 360K and 1.2M require different current level for
writing. 1.2M drives
will generally have a signal (pin6?) for choosing current
It was pin 2 on the original PC/AT 1.2M drive (I've just checked the
TechRef) and I would guess most clones did the same thing.
So, that will require a work-around.
(also, READY/DISK CHANGED signal was not completely standardized.)
AFTER coming out with the 1.2M drives, it bagan to be important to tell
them apart. So, getting it backwards?, they started embossing an asterisk
on 360K drives. So, any drive with an asterisk is 360K, a drive WITHOUT
an asterisk might be a 1.2M, OR might be a 360K from before they added
asterisks.
It's worse than that! IBM had 2 half-height 360K drives.
One for the PC/AT with a light grey panel. It has the asterisk. Made
by YE Data I think
The other for the PortablePC and PCr. Black panel, no asterisk. A Qumetrak 142.
I've got a PortablePC (5155) in bits on the bench at the moment. I
don't much like those Qumetrak drives to work on. I have the IBM
TechRef and the Qume service manual. Both contain schematics. The
schematics do not agree with each other, or with either of the drives
in my machine (which are both IBM labelled Qumetraks and are slightly
different....)
Quite why IBM used 2 different drives from different manufacturers I don't know.
-tony