Calibration of 8" floppy drive?

Chuck Guzis cclist at
Fri Feb 5 17:40:25 CST 2016

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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