29 Nov
1999
29 Nov
'99
11:44 a.m.
As a matter of fact, it's not unusual for floppy drives to lose their
alignment. What causes it is operating the stepping motor TOO SLOWLY. This
is frequently done in an effort to be conservative and allow the use of as
many different drives as possible, but the step rate is quite critical in
the long-term retention of alignment. Two alignment seem to go askew
frequently.
One, the most common, is index alignment. An alignment diskette has a pulse
or burst recorded nominally 200 microseconds after the start of the index
pulse, thereby allowing you or the technician to move the index sense LED
assembly once it's been loosened. I don't know why these get fouled up so
easily, but the vibration from running a 6 ms drive at 8ms might be at
fault. I'd say letting the springs POP the diskette out by snapping the
drive door open can do quite a bit to move the index sensor around.
Slamming the door shut won't help things either.
The radial alignment doesn't get fouled up as often as people think, but the
vibration I mentioned above is definitely the culprit, though rough handling
can cause problems as well. If you can hear your drive move its heads, as
you could with almost every PC FDD, then it's stepping too slowly.
Dick
-----Original Message-----
From: CLASSICCMP(a)trailing-edge.com <CLASSICCMP(a)trailing-edge.com>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Date: Monday, November 29, 1999 6:29 PM
Subject: Re: Needed: 1 IBM 8" alignment disk.
Try formatting
the disk. If you still can't read
back, an alignment disk won't help.
I'd be willing to bet that the Sykes hardware in question isn't
capable of formatting a raw 8" floppy. Remember, we're talking large
boards packed full of SSI TTL here, and the formatting functionality
usually wasn't present. (Besides, at the time all 8" floppies came
preformatted.)
Check that the head(s)
are clean and, if single sided, that the pressure pad is not
tilted. It is rare that the alignment is off unless someone
fiddled with it.
100% true. Unless it's been physically abused or someone decided they
needed to "tweak" the alignment, it's probably right where it should be.
And the advice to check the pressure pad is right on the money, too!
Tim.