Calibration of 8" floppy drive?

[Dan K]

>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.

Good point about this. One drive was quite smooth on that long lead
screw, the other was very stiff. I thought that it was trying to move
it and drawing too much current, leading to a shutdown or error state.
It loosened up with manual turning and I used some light machine oil
and worked it in. It now moves about as easily as the other, so I
don't think that this is still the issue.

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

I believe I probed these with my oscilloscope and verified they were
toggling, but it wouldn't hurt to check again.

>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.

Another great tip. This plagued me for a long time, until I realized
that I had only one drive connected, and it had the resistor network
IC unpopulated. I borrowed it from the other drive (they were on the
same wire, so I suppose that only one resistor network is necessary)
and that's what led to my initial success.

>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.

You're going right down the list of issues I ran into! One of the
pressure pads was nonexistent, but the other is in good condition. One
issue I had was that the head load plastic assembly that brings the
media in conformity with the sensor was broken and held together with
a twisty-tie. I used some CAD software to design a replacement and had
it 3D printed: http://www.vintage-computer.com/vcforum/showthread.php?49265-Owning-and-operating-an-S-100-bus-computer/page4

It seems to do the job, but I still don't have a replacement pad. That
seems to be okay however, because on one drive the head load solenoid
doesn't appear to come down far enough to push the disk very much. I
don't think I've ever seen the pad on either drive come down enough to
physically touch the disk--maybe just brushing it, barely. What might
cause this?

-Dan


On 2/5/16, dwight <dkelvey at hotmail.com> wrote:
> 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.
> Dwight
>
>
> ________________________________________
> From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Chuck Guzis
> <cclist at sydex.com>
> 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.
>
> --Chuck
>
>
>
>