>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 <dkel...@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-boun...@classiccmp.org> on behalf of Chuck Guzis > <ccl...@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 > > > >
