8 inch floppy head pad adjustment

Jeffrey S. Worley technoid6502 at gmail.com
Fri Oct 9 15:02:20 CDT 2020

I've not worked on 8" floppy drives, but have on tons of 5.25" single-
sided drives.  Older single-sided ones (usually 35-track from the 70's)
had load solenoids for the pressure pads, as with a double-sided unit.

The pad is to provide good contact between the media surface and the
head beneath.  I think older media must have ablated more than latter-
day media does, as it is rare to find a single-sided 5.25" drive with a
load solenoid.  The pad is always in contact whenever the drive door is
closed.  Double-sided drives of course retained the head-load solenoid
for some years, but eventually those were done away with.  So, I think
that unless you are using a drive 24/7, a pad in contact with the disk
should not be a serious concern.  That the pad IS properly in contact
is important of course, and pads should be inspected to see that there
is enough 'meat' left on them to provide the pressure needed.  Aft of
the pad, at the base of the head-sled pressure arm is a notch into
which the end of the spring rides.  Close examination of the sled will
probably show some higher and lower notches into which you can move the
end of the spring, to provide more or less pressure as needed, to tune
a particular drive.

In the old days, someone running a drive on a BBS or other heavy
application might wear a pad out.  We'd just steal one from a cassette
tape and stick it on the arm.  The cassette tape pad was square and the
originals were round, but it never seemed to make any difference.
 These days there are no cassettes floating around to cannibalize, so I
buy felt pads for furniture from Amazon, trim them with a razor and
stick them on a drive I'm refurbishing.  Atari, Commodore, Tandy...
 Many of the 80's 8-bits used this very scheme on their single-sided
drives and this solution is good for all of them.

I had someone insist to me recently that the felt pads I was buying
were acrylic and the originals were Rabbit Hair and that it was crucial
that the replacements be made of rabbit hair.  In practice, and that is
40 years of practice, any old pad will do just fine.  If it looks like
the right thing it will serve the purpose.   Just pick off  the old nub
of a pad and stick on your newly cut one and go.

Common faults I've been noticing are that disk drives made in the 70's,
80's, and 90's are failing in common ways.  I attribute these failures
mostly to lack of lubrication.  After 30 years they get a bit gummy and
the actuators have to work harder to move the head sled, which puts a
greater load on the darlington drivers which power the actuators, which
causes the drivers to fail.  Replacing the drivers will often restore
the drive to working order, but they will fail again in short order if
the original probelm is not resolved.  I simply clean the rails and
stepper bands, touch a little wd40 to the rails to free the head sled,
cycle the head back and forth a buncha times manually to exercise it
and distribute the lubricant, then follow that will a little white
lithium grease for a longer-lived lube.  Not only will the drive run
better and a lot quieter when lubricated, the loads on the actuators
and their associated electronics are greatly reduced, making for a
like-new drive.

The second thing that is happening quite often is electrolytic
capacitors are failing, leaking or not.  I had a pair of drives the
other day which made quite a racket when spinning free even without
media installed.  Replacing the electrolytics on the spindle motor's
board got rid of the noise and made it possible to properly tune the
RPM's, which had been just all over the map.



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