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Thread: Tandon Full Height drive troubleshooting..

  1. #11
    Join Date
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    That's what I was saying about head supports--they're very delicate and ham-handed cleaning can damage them. I suspect that it's what happened--one head or the other isn't making consistent even contact with the medium, so you get the 'wavering signal".

    The other possibility is that the clamping cone is damaged somehow and the disk isn't being seated correctly.

  2. #12

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    Quote Originally Posted by alank2 View Post
    I don't have one - I used a Q-tip carefully with isopropyl alcohol.
    Everybody who works with floppy disks should have one for each size floppy in the inventory. I figured this out thirty years ago and have never looked back. I have never had a drive damaged by a cleaning disk and I've gone through thousands upon thousands of floppy disks so it's inevitable that some would foul drive heads. It's not only safer but also far easier and only takes a minute or less with no disassembly required.
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

  3. #13

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    Sounds like good advice guys, I'll have to be on the lookout for some cleaning disks. Both drives are working and installed now, so I think the radial adjustment just needed to be tweaked a small bit.

  4. #14

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    One more thing, as the "wow" you described could be due to the diskette media spinning slightly off-center, be extra careful when inserting diskettes when the motor is not running. Be very gentle about closing the hub down on the center hole.
    - Doug

  5. #15

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    Thanks Doug, will do. I ordered a cleaning disk off eBay so I'll have one for next time. I'm just happy to have both drives working!

    Now if I could figure out the video jitter issue - I have to think it is in the logic somewhere. What is happening is that it introduces what looks like horizontal jitter on various rows of pixels. It begins on a few rows and spreads to most of the the screen and then can disappear. Any idea which IC's are responsible for this?

    I'm going to try to do the 5 MHz mod tonight, I wonder what its effect will be on the screen jitter issue. Not sure if the EEPROM/CPU are rated for 5MHz yet, will have to check those.

  6. #16

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    Previously I got the impression you were seeing a "squeezing" of the screen? This jitter sounds like something different. Sounds like something is affecting the dot-clock, but for it to only affect certain rows is very strange. And to be consistently affecting certain rows is even stranger. Could it be related to certain patterns in those rows? Like more "on" pixels (periods)? I'm wondering if some electrical issue (hi-resistence contact, etc) might be causing clock issues with the rows, and it is the "data" (dot pattern) that is influencing the clock issue.
    - Doug

  7. #17

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    It has the squeezing issue too, when the drive motors kick on. I'll try to get some video of this the next time it happens, maybe that will identify what is going on!

  8. #18

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    Think thing that the "squeezing" makes me think of is drooping voltage, or possibly interference, related to a high current spike when the motor tries to start (perhaps because of the spindle not well lubricated). Or possibly related to bad contacts (high resistance) along the power supply paths.
    - Doug

  9. #19

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    I agree and it seems to be the +12V rail. it is normally 11.5V and drops to 11.3V momentarily. I wonder if I should go back to the power supply and try to tweak it up to a more solid 12V, maybe that little drop wouldn't cause an issue then. I polished the contact pins with an erase and applied a little Deoxit. The monitor board is funny though, there is a connector, but all the pins are on the underside of it. I've moved/rocked it a bit, but don't want to pull the video board to try to clean them [yet].

  10. #20

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    I got the 4 MHz tweak done last night. Put a toggle switch in the back cover between the heat vents that switches between 4 MHz/2.5 MHz. I tried the 5 MHz, but it didn't seem stable and it sometimes loaded the COPY program and other times failed. 4 MHz seems to run solid though and is a huge improvement over 2.5 MHz. I don't think it made any difference with the video jitter issue however, I think I saw some of that in 4 MHz mode too.

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