[fdutils] Need help with weird floppy issue

Donnie Barnes djbarnes at gmail.com
Mon Mar 20 02:13:50 CET 2006

Okay, with a lot of work by Simon Owen, we've got a lot of useful data, but
more importantly I've been able to write this floppy image with a Windows XP
machine and his utility.  It worked and allowed me to make a couple backup
images on the System 24 machine itself.

While I have been able to burn an image with a PC, it's still a bit
unreliable (very finicky about what controllers will work, what drives, and
what media).  But it's way better than nothing as my game now plays.  :-)

That said, the only floppy drive that would copy an image in the machine
itself was an OEM unit.  Four other floppy drives would not.  Some of them
would boot and run the game, but none would copy.  The pattern I've isolated
as to why some work and others don't is no surprise...it's speed related.
The slower drives work better.  The slowest is that OEM drive from the
System 24 machine.

So I want to hack a drive to slow it down.  I've tried following your
advice.  I have a drive that looks a lot like what you have pictured,
including a component at the same basic location that's labeled with a 492
on it.  Obviously that's the resonator.  So with the drive running
floppymeter, I took my oscope and hit both pins on that resonator.  I got
something ugly-ish on one pin, but on the other I got what appeared to be a
1V sine wave that was about 492khz.  Great.

So I removed the resonator (yes, I know how to solder and desolder :).  I
then connected wires to each solder pad where the resonator was (just in
case I needed something at the other side).  But now I'm not sure what to
do.  I attached the ground side of my signal generator to the chassis of the
drive.  I attached the hot side of the signal generator to the wire on the
side where I found the signal before.  I then attached my oscope in parallel
with this and could see my signal.

But booting the linux machine with this drive attached and then running
floppymeter gets a pause, then some kernel errors ending with a floppy
driver timeout.  Never see the motor even try to spin.  So obviously I'm
doing something wrong.  Any ideas?


On 3/8/06, Uwe Teetz <mhteetz at aon.at> wrote:
> Hi Donnie,
> I found an even better solution, put an AM (455kHz) LC IF filter and a
> capacitor in place of the ceramic resonator. Mine worked fine, adjustable
> from 400 to 600 kHz the motor following the in speed.
> If you recycle a filter from an old radio, look to it from the bottom, it
> should have a capacitor build in and connected to two of the mostly five
> pins. Use those two. Very common are the outer two pins on the side with
> three pins.
> I will do some testing with the floppymeter later on.
> Uwe
> ----- Original Message -----
> *From:* Donnie Barnes <djbarnes at gmail.com>
> *To:* Uwe Teetz <mhteetz at aon.at>
> *Sent:* Wednesday, March 08, 2006 3:19 PM
> *Subject:* Re: [fdutils] Need help with weird floppy issue
> On 3/8/06, Uwe Teetz <mhteetz at aon.at> wrote:
> >
> >  Hi Donnie,
> >
> > to the motor speed:
> >
> > the 3 phase syncron motor controller has a ceramic resonator as
> > reference -> nothing to adjust.
> >
> >
> > Many of my drives here use 492kHz and 491kHz resonator. This slight
> > difference will not help. For testing I removed the resonator and feed to
> > one pin a signal from an extern oscillator with 1V~ output (you have to try
> > which one is the input to the controller) See pic2. I could regulate the
> > motor from half to double speed easily.
> >
> > You could also try to replace the ceramic resonator wit a 455kHz
> > resonator used as IF filter in AM radio receiver or put one small RC
> > oscillator in to the case. RC oscillator (potentiometer adjustable) samples
> > are plenty in the net.
> >
> I've got a pretty crappy (compared to yours) signal generator that may do
> what I need.  If not, I can certainly build an RC oscillator.  Looks like
> you had yours set to sine wave, but I suppose I'll take a peek at the signal
> off the oscillator on the device with an oscope.  I assume I just need to do
> floppy access on the PC to make it spin, right?
> Thanks for the great info!
> --Donnie
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