Re: How to adjust the speed of floppy drives?

[mjmahon@aol.com (Michael J. Mahon)]

Ernest wrote:

>I have a couple of "hacked" disk ][ style drives that are no longer working.
>I'm not exactly sure of what the problem is but I think that the speed
>adjustments are off. The former owner moved the adjustment pots to the
>front of the drive because (according to him) the drives needed to be
>adjusted frequently and he was tired of having to take the drives out to
>adjust them. The drives also have Write Protect toggle switches and the
>red/green lights on the front too (also added by the former owner.) I don't
>want to toss the drives out if I can repair them but I'm not sure how best
>to do it.

The usual reason for wanting a convenient speed adjustment was to
copy disks protected by nibble-counted tracks.  In normal use, it is
practically never necessary to adjust disk speed.

>I don't have a strobe light for adjusting them, and they are not able to
>read any of the speed utility disks for adjusting the drives by hand. Is
>there a way to adjust the drives by small amounts to see if I can finally
>get them to read a disk? Can I adjust the drives on the fly, while a disk
>is spinning in the drive, or do I have to power down between adjustments? 

It sounds like they are pretty far out of adjustment--the main downside
to having a front-panel speed adjustment is that little fingers like to
twiddle knobs.  ;-)

You don't need a strobe light, just a flourescent light will do.  Just turn
the speed adjustment slowly until the appropriate (60Hz) band appears
to stop rotating.  (Even a small, bright incandescent lamp can make the
bands visible--it has to do with how light the filament is, so that it can
change brightness significantly within 1/120th of a second.  For example,
a night light illuminating the flywheel in a relatively dark room also works.)

BTW, if they are _really_ far out of adjustment, there may be more than
one adjustment setting that causes the ring to appear to stand still.  In
that case, try the one closest to the middle of the adjustment range, then
--if it doesn't work--try others.

>Or, does anyone want to adjust the drive speeds for me, for a reasonable
>price, if I mail them to you?

I think you can do it yourself without much trouble.  This is a useful skill
for a collector of old gear.  ;-)

Report back if you have any trouble--or even if you don't!  ;-)

-michael

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