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Thread: Testing and/or troubleshooting Model III floppy drives

  1. #1
    Join Date
    Oct 2019
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    Richland, WA (USA)
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    Default Testing and/or troubleshooting Model III floppy drives

    Hello, I am trying to get the disks working in a Model 3 which I bought from a friend as a child, and recently brought home from my parent's house.

    As a kid, I never had disks for it until a kind soul mailed me one all the way from Australia! Much to my disappointment at the time, I couldn't get it to work and soon gave up. Now that I have a little more patience, a little more dexterity, a little more electronics knowlege and a little more budget I would like to get to the bottom of this! [Though some emphasis is deserved on the "a little" on all preceding accounts ;-]

    I had ordered some X1 capacitors and so tonight I opened up the case to replace them and try refurbish the floppies, but noted the following:

    - there is a single power supply, labeled "Compaq Computer Corp, Copyright 1987" with some very aftermarket looking cabling
    - I pulled a floppy drive out, thinking I would try moving things along the rails like I had seen in a YouTube video. But nothing seemed readily accessible and so I figured I should do some more homework (at least re-watch https://www.youtube.com/watch?v=-p2GkL9fjV8) before fussing with them.
    - Powering the computer on with the drive re-connected to power, I did notice that neither of the 50Hz/60Hz markings seemed to stand still under a newer incandescent bulb.


    I have a Model 100/200 floppy that I threw onto an (otherwise-unrelated) order of Model 100 parts from arcadeshopper. When I put that in, the machine fails to boot at all — the disks spin for a while, then turn off, still blank screen. If I leave the door open I do get a "Diskette?" message. When hitting Break+Reset to boot into ROM BASIC, `OUT 244,1` turns the LED on for the bottom drive. Both spin (?). `OUT 244,2` turns the LED on for the top drive. Again, both spin. No other noises, i.e. besides the spinning there's no clicks or clatters like e.g. our Apple /// used to do.

    I need to dig around and see if I can find the TRS-DOS disk in some boxes, but it didn't work ten years ago and I'm not hopeful it will again. How might I proceed in troubleshooting? Do I risk damaging disks by trying them? Are the drives relatively robust if I open them up and try clean/move the mechanisms manually?

    As far as making disks, is the process in https://www.youtube.com/watch?v=JM_eW7h07ew pretty foolproof if I pick up any random [update: 360K as stated in video] 5.25" drive off eBay and chuck it in an old Windows XP machine? I don't want to be troubleshooting the Model 3 drives if the disk itself isn't "known good".

  2. #2

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    I'd start off by cleaning and lubing the rails and using a head cleaning disk. I've had the setscrew for the stepper motor loosen up on many Tandon and Texas Peripherals drives, so check those. It's behind an open square in the frame and may have a clear plastic window over it.
    As far as adjusting drive speed...the strobe effect isn't going to work with an incandescent bulb. You need an OLD fluorescent bulb. Anything modern like CFL won't work for some reason. When I was a kid I used to use my fluorescent desk lamp but that disappeared over the years. I found that a small neon sign from my game room works great.

  3. #3

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    The first step should be to use the head cleaning disk mentioned above. It is the most like procedure to achieve results without the danger of damaging any hardware components.

    Make copies of any disks you will use so that you won't run the risk of damaging the original or last one.
    PM me if you're looking for 3½" or 5¼" floppy disks. EMail “ ” For everything else, Take Another Step

  4. #4
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    What is the model number of the floppy drive? If you have an after market PSU, the drives may be third-party, too. There's a lot of info on the web, but it's very much vendor and model specific.

    You can make real floppies from images using an old DOS-based machine (no higher than Windows 98 ). I use a Pentium 233MMX machine and a TRS-80 emulator written almost 20 years ago by David Keil. Depending on the images, there are different software tools that can be used.
    Last edited by lafos; October 24th, 2019 at 04:41 PM.

  5. #5

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    Quote Originally Posted by Stone View Post
    The first step should be to use the head cleaning disk mentioned above. It is the most like procedure to achieve results without the danger of damaging any hardware components.

    Make copies of any disks you will use so that you won't run the risk of damaging the original or last one.
    And don't forget to make a copy of the cleaning disk for future use ... ok I´m making jokes

    There are many videos on Yt how to clean a disk drive. The 50Hz/60Hz markings are important if a drive isn´t really working. Usually the disk drives are reliable. Try to use a boot disk after cleaning the drives. If everything is ok then there is no need for checking the rpm. The disk's head can be moved manually during the cleaning process with care but without power on.
    Deutsches TRS-80 Forum ‹(•¿•)›

  6. #6
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    Thanks for all the tips so far! I've ordered both a cleaning disk (which I suppose I don't necessarily need if I have the drives apart anyway) and a fresh bootable disk off of eBay, and I hope to carefully open the machine again this week or next and give it another go.

  7. #7
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    Got back to this project tonight, took the machine all apart again and opened up the floppy disks this time! Here's what I know:

    The drives each have a "Texas Peripherals" sticker on the frame bottom, and 99-5050-001 Rev C Tandy Corp c 1980 on the mounted PCB. The head mechanisms were a bit scratchy on their rails but not seized or particularly griming. I swabbed them down a bit and added some fresh Wahl clipper oil that I had handy. They are now less scratchy, though not silky smooth.

    The top drive had one of it's little white door latch pins missing this time I checked it. The little grabber it would have clipped into was also cracked. I superglued that and stuck a toothpick in place of the for now but haven't dared test the joint yet. (I'm usually 50/50 at _best_ for superglued plastic holding up more than 0 seconds of real usage…)

    The bottom drive had a more interesting problem! I noticed it had a gaping hole above the drive head where the other one had an insert. AFAICT this is a plastic piece with some sort of felt attached, and I imagine this must be to push the medium up against the head. So maybe we can't expect that drive to work. (Oddly this drive has two metal posts for its door latch, rather than one metal post plus plastic pins?!)

    So I took the [formerly] top drive, replaced its latch with the sturdier one, and installed it in the bottom slot. The [formerly] bottom drive back in up top, with its latch still flapping in the breeze for now. I also re-seated all the jumpers around the PCB on both drives just for kicks. But alas:

    Still nothing


    Questions:

    - what are the chances I could find the missing part? does it have a name? I suspect parts are rarer than the drives themselves though?
    - am I correct to assume that the cable position will select the primary drive? is there any other termination or configuration that I'm overlooking in order to swap the two drives?
    - should I be hearing the head grinding and clicking a bit before and/or after I close the door on a disk?

    From the video in my OP, I learned that I should leave the door open at first, then close it when I get the "Diskette?" prompt. With no disk, I get no prompt just a black screen. With a disk in but latch open, I get the "Diskette?" prompt. After I close the latch, nothing changes…it just spins and spins for a while with no apparent attempt to sync up with the tracks. It doesn't click or grind or any sort of "seeking" noises, just spinning. What should I test or try next?

  8. #8
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    As far as the Drive Latch is concerned, there are folks that have designed the Door Latch Parts
    for Texas Peripherals and the Tandon TM-100

    You just need to locate someone with a 3D Printer or Resin Printer to print some SPARE Door Parts.
    You can get some Brass Brazing rod in 1/8" and 3/32" sizes and cut some Brass Rod to make a full length
    Hinge part. Toss those small White Nylon pins in the TRASH, and insert the full length Brass Rods
    for a Hinge that will outlast you. Most older Floppy drives came out with the Brass Pins, at least the
    Tandon TM-100 series did.

    You can wipe down the Guide Rods that the Head carriage assembly slides on with A Cotton Swab
    dipped in Alcohol. I use a Motorcycle Lubricant called Dri-Slide (which doesn't attract dirt) to lubricate
    those Head carriage assemblies. (It's also good to use on flatbed scanners). Any Motorcycle shop
    should carry the Dri-Slide, and a bottle will last you a lifetime.

    I have a Basic RPM Test Program that works on the Model 3, but you need to load it from Basic.

    Probably the best way to test the Floppy drive is to remove it, and connect it to an old DOS Computer.
    Then download Dave Dunfield's Imagedisk and use the Utilities to check the RPM, and step the
    head back and forth as a test.

    Cable Position - Some of the TRS-80's had Pins removed from the Cables to make sure you plugged
    the right floppy in the right position. But, the Drives that are Internal need to be strapped for Drive Select 0
    and Drive Select 1. That is typically a punch out header strip that is located on the Floppy. I've removed
    those and installed Dip Switches, so it makes it easy to change positions. The Model 3 and 4 does not
    use the Terminators on the (Internal/External) Floppy's. But, typically all other computers use a Terminator
    (DIP Package) on the last Floppy on the End of the Cable. I know that is true for the Model 1.


    Thanks.

    Larry
    Last edited by ldkraemer; November 23rd, 2019 at 04:43 AM. Reason: no terminator

  9. #9
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    Richland, WA (USA)
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    Appreciate the door latch tips! To be clearer, the "missing part" I am concerned about is this:

    > a gaping hole above the drive head where the other one had an insert. AFAICT this is a plastic piece with some sort of felt attached, and I imagine this must be to push the medium up against the head.

    I didn't quite dare take the insert out of the more complete drive for fear of snapping it, but it looks like more than just plastic. Has anyone had success replicating that part?

  10. #10
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    Small update: last night I replaced the cable between the main board and the disk controller. The old one was definitely decaying but after I took it out did have continuity on all lines. No improvement, no change with the new cable. Get the "diskette?" on boot followed by black screen soon after I close the drive doors. No head seeking movement/noises.

    Unless someone knows a common cause for that symptom, I guess the next step is to start studying the service manual for all the details of how these drives and controllers are supposed to work. I do not have any old DOS computers handy although possibly a Tandy 1000 which might be a fun combo if I can find it in working condition itself. I wasn't sure how widely compatible these drives were but am getting the impression they were quite similar at the interface level at least.

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