Calibration of 8" floppy drive?

dwight dkelvey at
Fri Feb 5 19:03:25 CST 2016

If belt driven ( suspect most 8 incher are ), make sure
the pulleys are smooth and clean.
Often old belts will lose a little small lump of rubber that
stick to the pulley. This will cause mis-reads.
Make sure the belt is tight and not slipping.
The pressure pad can get lumps on it from disk crud.
The pad must be flat. It can not be cleaned with a
clear disk that is double sided.
Solvents don't work well. I often find a dull knife edge works
well to get crusted gunk off.
The rest, Chuck had stated. Don't mess with
tracking or fiddle with pots that you are not setup properly
to adjust.

From: cctalk <cctalk-bounces at> on behalf of Chuck Guzis <cclist at>
Sent: Friday, February 5, 2016 3:40 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Calibration of 8" floppy drive?

On 02/05/2016 01:58 PM, Dan K wrote:

> So, how do you deal with your 8" drives, and what do you do when
> they don't work?

I've got both the FDD-100s and the double-sided cousin, the FDD-200.
They're very similar in construction; good German engineering, cast
metal faceplates, etc.  They really should not be drifting out of
alignment.  Bitsavers has some useful documents on them.

First off, IIRC, these are leadscrew-type positioner drives.  One issue
dogging these is that grease on the leadscrew can get filthy with dirt
or harden, preventing smooth operation of the positioner.  Make sure
that the leadscrew is clean--use a mild solvent such as kerosene if it's
hardened.  Re-lube with a lightweight grease or oil--you just don't want
the carriage to "stick" in its travel.

Make sure that the track 0 sensor is clean--the same for the index sensor.

Remember that floppy drive bus topology is open-collector, which implies
that the "receiving"  (far) end be terminated with a pullup resistor
(usually 150 ohms to +5 on 8" drives).  Very often, this is in the form
of a DIP resistor network.  If you're missing it, operation is going to
be erratic.

Since you're dealing with single-sided floppies, check the condition of
the side 1 pressure pad--the glue on these often dries out and the pad
falls off.  The pad itself resembles a billiard cue tip.

Don't get into the alignment issue without a scope and an alignment
disk--once you loosen the stepper motors, it's a very touchy operation
getting them back into position, even with a special (expensive)
alignment disk.

Hopefully, this will get you started.  Just remember that dirt in any
disk drive is the Devil's playground.


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