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Thread: Tandon Full Height drive troubleshooting..

  1. #1

    Default Tandon Full Height drive troubleshooting..

    I've got a Kaypro 4/83 with one drive that is solid, but the other drive has intermittent problems. It will read okay sometimes, but then fail with bad sectors.

    I pulled the pcb's off of it and re-wet the solder joints with some flux to make sure there wasn't any cold/old joints, but this did not change the issue.

    I saw this page:
    https://www.classic-computers.org.nz...ive-repair.htm

    So I decided to try my luck with a scope an the test points. I used a Realistic tape erase to bulk erase a disk, then I formatted it on my 5170's 360K drive so hopefully it has 40 nice clean written tracks. I then wrote a quick CP/M program that I can direct to read track X for X times.

    The good drive produces Vpp of 530mV, but the bad drive does an odd thing - it produces Vpp of 350mV to 450mV - but it wavers between the 350mV and 450mV as the disk spins.

    Any idea on what that means and what can be tweaked to get it working like the good drive?

  2. #2
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    Can one assume that you've cleaned and inspected the heads?

    Are the head supports damaged?

  3. #3

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    Hi Chuck,

    Both drives have had their heads cleaned, but looked okay (as far as I can tell).

    I've tried the radial track adjustment on the bad drive. The bouncy signal at track 0 can be improved to much less bouncing with a small adjustment. That small adjustment on the other side (track 79) reduces the amplitude for each channel to 250-270mV from perhaps 300mV (when it was bouncy at track 0). These voltages are only half of the voltage (not A-B, but just A).

    Thanks,

    Alan

  4. #4

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    I think it might be fixed! I can compare disks using the COPY utility with no errors, swap the disks, and verify again with no errors. Signals look better on a disk written by the drive than the disk I wrote in the 5170. Side 0 is stronger than side 1 for some reason.

  5. #5

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    Can you tell what the "wavering signal" is synchronized to? For example, if you trigger the scope on the index pulse, does the wavering vary or lock-on? I'm not familiar with the drive electronics, but wonder if there might be a floating ground or such thing, and the drive motor - or some other source - is causing interference. Or else there's a power supply filtering issue, and the ripple is from the line (60Hz).
    - Doug

  6. #6

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    Quote Originally Posted by alank2 View Post
    I think it might be fixed! I can compare disks using the COPY utility with no errors, swap the disks, and verify again with no errors. Signals look better on a disk written by the drive than the disk I wrote in the 5170. Side 0 is stronger than side 1 for some reason.
    So, if the signal is better when written on the drive, that suggests head alignment. It may also be possible for the heads to get knocked off "square" - which might also make "foreign" diskettes harder to read. That could also explain the reduced, and variable, amplitude of the signal.
    - Doug

  7. #7

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    I'm sorry Doug, I don't mean wavering in frequency, I mean amplitude. It seems to be synchronized to the revolution of the disk so maybe one cycle would be it going from 350mV to 450mV and back to 350mV again. At least that it what I think. The radial track adjustment seemed to fix it though, much less wavering with only a small adjustment. Would the radial adjustment being off cause that type of thing?

  8. #8

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    The bottom head is on a plastic mount and is quite fixed, but the top head is very loose and floating, both drives seemed okay when I was cleaning them.

  9. #9

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    Sounds like you didn't use a disk to clean them.
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

  10. #10

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    I don't have one - I used a Q-tip carefully with isopropyl alcohol.

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