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Thread: Tandy 2000 FDC chip question

  1. #51
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    That "IC" is a 150 ohm resistor array, which should be fine. That drive goes on the end of the cable.

    The fact that the drive didn't work when it was installed in your Tandy 1000 still concerns me so far as the health of the drive goes. Did you have the terminating resistors set up properly when you tried it? If either both or neither drives had them that could cause issues.
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  2. #52
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    If you're only working with a single drive, that one must have a terminator (the DIP in the blue socket near the edge connector).

    Your first drive should be set to DS0 and the second (B) should be set to DS1.

    Although most people don't think of it that way, the floppy connection is a genuine bus.

  3. #53
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    Okay.

    Well I've tried both singly, set to Drive 0, terminator installed (swapped between them for testing), and they both do exactly the same thing, as in my original video. Over an over again.

    I see nothing that suggests they are trying to seek Track 0 at all.

  4. #54
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    Also.. I'm not sure if I demonstrated anything useful by doing this and hopefully didn't harm anything by doing so, but I used a jumper to bridge pin 7 and 13 on U135 briefly at boot time. When the system attempted to boot, the head moved all the way out, away from the hub. It doesn't begin reading from there though, it just kind of stays there until I release the jumper and then it resumes doing as before.

  5. #55
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    Quote Originally Posted by kb2syd View Post
    My guess is that the ROM is corrupted. The 2K does not have a BIOS on board, it loads it from the disk. The ROM is pretty simple too, set up the FDC and load contents from disk, then execute.

    I would dump it and compare it to some of the ones available online.
    Is that who I think it is? Wow, must have been a million years since we saw ya.

    Sorry for the interruption. Please continue ...

  6. #56
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    You can check the operation of the floppy drive independently of the computer, if you have a power supply and a few test clips. Basically, you apply power and ground the configured drive select. You can ground or leave floating the Direction pin (depending on which way you want to go) and tap on the Step pin with a probe connected to ground. It's not necessary (IIRC) to have a disk in the drive or the motor on. You can watch the carriage move as you tap.

    Alternatively, you could build your own drive exerciser box with a few components.

    The great thing about floppy drives is that they're very simple, brain-dead, mechanisms.

    (I assume you checked the level of the +12 supply line; I may have forgotten to add that)

  7. #57
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    Thanks Chuck.

    Yes I checked the 12V it looks just fine.. it's coming up about +11.89V and seems pretty stable.

    I may try what you've suggested there with testing the drive. I did install it in a few generic PCs.. but could not figure out what BIOS setting to use. The only one that would allow the machines to boot with one of the T2000 drives as Drive B was if i set it as a 1.2mb 5.25. If I do that, it does the normal drive init motion (where the head moves back and forth with that 'waa-waa' sound as the BIOS checks it) that the 1.2mb drive I have in there as Drive A also does. I'm really thinking head control, at least on the drive itself, is not the issue here.

    One question.. I understand the 7414 that is part of the Track 0 circuit is a hex inverter with Schmidt trigger. Does that mean I should always expect the input and output of each inverter to be exactly opposite? Or can other things in the circuit act on them to change that? Right now I have a high logic signal on both pins 8 and 9.

  8. #58
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    Answered my own question.

    The answer is no - that 7414 has a bad inverter. Swapped out.. voila.. it boots. Track 0 matters, apparently.

    Thanks for all the help everyone. Now I can get my Netronics machine to this makeshift bench and try to solve the mysteries of non-loading BASIC there.

  9. #59
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    Glad you worked it out. Have fun!
    FWIW, if you want to try that 2K drive on a PC, just call it a 3.5" 720K.

  10. #60

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    Quote Originally Posted by tipc View Post
    Is that who I think it is? Wow, must have been a million years since we saw ya.

    Sorry for the interruption. Please continue ...
    It's me. Call sign is different but same old Kelly. Been laying low for no good reason.

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