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Thread: 8 CDC Floppy Drive Repair

  1. #11

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    Here I am again. I’ve completely repaired the drive, new belt, capacitors and everything. I also crimped my own IDC cable to connect to my Zenith Data Systems Z-100. The drive powers up and the spindle rotates, and if connected to the computer and a disk is installed, the head “clamps down”. However, the computer doesn’t recognize the drive in Z-DOS at all. I’m not exactly sure what to do, and there is a 4 switch block (red block in the 3rd picture) on the drive PCB. The head motor seems to want to move, as it rotates just a fraction, but doesn’t move any further. I can move it with my fingers, but it definitely has some resistance. Any ideas on what I can do?
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  2. #12
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    See here, page 31 (PWA diagram). Note that you have 4 DIP switches instead 4 shunts. One of these needs to be closed to access the drive. On PCs, this is normally the second drive select, but I'm familiar neither with your cable nor with the Z100, so your mileage may vary.

  3. #13

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    Thanks, that’s helpful. I must have missed that when I read the manual earlier. I have, however, closed one of them and didn’t get much progress. I’ll try again with each one tomorrow, but I’m not sure which address I’d need. The cable is just a 50 pin Shugart card edge connector to a 50 pin IDC connector that I put together myself. I’m not exactly sure if software could be an issue, either. The computer runs Z-DOS, which is Zenith’s version of MS-DOS, but I also happen to have an IBM compatible MS-DOS that runs on my Zenith. I’ll try that with the drive also.

  4. #14
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    You'll have to figure out which drive select the Z100 expects--that's something I've never fooled with. If you get nowhere, there are some things we can try.

  5. #15
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    If it's the only drive on the cable, why not close all 4 drive select switches for now.

    Touching a grounded wire to the STEP pin (36) of the interface should move the head; if not, try it with the DIRECTION pin (34) grounded.

    Congratulations on getting this far; how did you ever manage to find that belt?

  6. #16

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    Quote Originally Posted by MikeS View Post
    If it's the only drive on the cable, why not close all 4 drive select switches for now.

    Touching a grounded wire to the STEP pin (36) of the interface should move the head; if not, try it with the DIRECTION pin (34) grounded.

    Congratulations on getting this far; how did you ever manage to find that belt?
    Once I get home today, I’ll try your trick for moving the head. I had tried to close all four switches, with no luck. Maybe there’s something else going on?
    As for the belt, I was able to get it with lots of luck. A company called Compro Computer Systems somehow had 11 of the original belts in stock, and I just received mine yesterday and it works great.

  7. #17
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    A lot of what Mike said holds true in general. To test the accessibility of the drive, you don't need a computer at all--just by grounding various inputs you can observe the function.

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