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Thread: Testing and/or troubleshooting Model III floppy drives

  1. #1

    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 3" or 5" 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 Im making jokes

    There are many videos on Yt how to clean a disk drive. The 50Hz/60Hz markings are important if a drive isnt 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 () TRS-80 Knowledge Archive (please have a look at the Photos & Files sections there) starting December 14, 2019 Yahoo Groups will no longer host user created content on its sites

  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.

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