Do we know the make/model of this drive?
----- Original Message -----
From: "Marc Verdiell" <marc.verdi...@gmail.com>
To: <cctalk@classiccmp.org>
Sent: Saturday, August 22, 2015 12:50 AM
Subject: RE: 5.25 floppies that read but don't
write
Chuck,
I looked at the pin 2 signal and resulting drive
behavior. It doesn't
properly auto-switch between densities as it
should. It does switch it for
reading, but not for writing. Below is the full
story.
There is one jumper that controls DD/HD
switching mode.
In the auto position, I can read both HD and DD
formats (I use the right
diskettes for either format). You can see the
computer on pin 2 (density
select) trying both positions, settling on the
right one (high for HD, low
for DD), and reading the disc correctly.
That's great. But when writing, although pin 2
goes to the right level, the
floppy seems to ignore it. It will always write
at DD, and refuse to write
in HD (no signal at the head).
Interestingly, in the fixed density position
(should be HD only), it WILL
write at 1.2M HD! The write signal does appears
at the head. Unfortunately
in this setting it will NOT switch the reading,
get stuck reading only DD
and fail on HD.
So I can either have the reading HD or the
writing HD, but not the two at
the same time. That's why a regular format
fails. The density switching
logic seems to have a problem. Rather than track
down which IC or transistor
failed on the board it might be much simpler to
get another 5.25 floppy. In
the meantime my understanding of these simple
critters has improved a lot.
Marc
At high density, have you taken a good look at
pin 2 of the floppy
interface? Have you checked to see if pin 2 is
configured (via jumpers)
as "density select"?
--Chuck
