8 inch floppy head pad adjustment

[Paul Berger]

The big difference is most 8" drives had AC motors that turned the 
spindle all the time so if a diskette drive was loaded it would turn all 
the time and if the head(s) where loaded it would wear a groove in the 
media, hence the head load solenoid.   Most 5.25 and smaller drives have 
a DC motor that is only turned on when you are about to read or write 
the diskette so leaving the heads loaded is less of an issue.

Paul.

On 2020-10-09 5:02 p.m., Jeffrey S. Worley via cctalk wrote:
> 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.
>
> best,
>
> Jeff