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FDC HW Failure Diagnosis

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  • coryklatt@rocketmail.com
    I ve been trying to diagnose a failed TI floppy drive controller. When I set CRU bit 1 to 0 the controller responds by turning on the LED, however, it fails
    Message 1 of 2 , May 8, 2011
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      I've been trying to diagnose a failed TI floppy drive controller. When I set CRU bit 1 to 0 the controller responds by turning on the LED, however, it fails to load the ROM into >4000. Mem inspection reveals all 0s.

      I've tested the voltage points on all chips including the 1771, the ROMs, the special control chip (to the left of the ROMs) and all other chips. I've traced most lines for continuity breaks revealing no breaks. I've tested both regulators and they are within spec.

      I pulled all Caps and resisters and they all appear to be in spec. Although on this point -- most of the .01uf caps used for the buffers read 10nf, but 2 or 3 rate as low as 9nf and a couple rate 12nf. I'm guesing this is in range given that the voltages appear ok.

      Does anyone have some suggestions on where to go from here. I'd love to use a logic probe to trace what occurs when I set cru bit 1 to 1, but I'm not 100% where to test.

      Does anyone have a broken FDC that I could have or borrow to swap out some chips?

      Thoughts or ideas? I'm doing this for my personal education and appreciate any tips, pointers, and mentoring.

      I should also point out that the drives do spin up on power on of the PEB, however setting cru bit 2 to 1 doesn't appear to pulse the drive, but I'm not 100% sure I've performed the test correctly.


      All the best,

      Cory
    • coryklatt@rocketmail.com
      Corrections to my prior post: Setting CRU bit 0 to 1, turns on the LED on the card, however, fails to page the DSR into 4000. Setting CRU bit 1 to 1, fails to
      Message 2 of 2 , May 9, 2011
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        Corrections to my prior post:


        Setting CRU bit 0 to 1, turns on the LED on the card, however, fails to page the DSR into >4000.
        Setting CRU bit 1 to 1, fails to pulse the drive motor.



        --- In ti99-4a@yahoogroups.com, "coryklatt@..." <cory.klatt@...> wrote:
        >
        > I've been trying to diagnose a failed TI floppy drive controller. When I set CRU bit 1 to 0 the controller responds by turning on the LED, however, it fails to load the ROM into >4000. Mem inspection reveals all 0s.
        >
        > I've tested the voltage points on all chips including the 1771, the ROMs, the special control chip (to the left of the ROMs) and all other chips. I've traced most lines for continuity breaks revealing no breaks. I've tested both regulators and they are within spec.
        >
        > I pulled all Caps and resisters and they all appear to be in spec. Although on this point -- most of the .01uf caps used for the buffers read 10nf, but 2 or 3 rate as low as 9nf and a couple rate 12nf. I'm guesing this is in range given that the voltages appear ok.
        >
        > Does anyone have some suggestions on where to go from here. I'd love to use a logic probe to trace what occurs when I set cru bit 1 to 1, but I'm not 100% where to test.
        >
        > Does anyone have a broken FDC that I could have or borrow to swap out some chips?
        >
        > Thoughts or ideas? I'm doing this for my personal education and appreciate any tips, pointers, and mentoring.
        >
        > I should also point out that the drives do spin up on power on of the PEB, however setting cru bit 2 to 1 doesn't appear to pulse the drive, but I'm not 100% sure I've performed the test correctly.
        >
        >
        > All the best,
        >
        > Cory
        >
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