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Thread: An IBM 5150 that won't IBM 5150

  1. #1
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    Default An IBM 5150 that won't IBM 5150

    So, I've picked up a IBM 5150 at VCF Midwest earlier -- 64-256k. It was tested and demonstrated to work prior to my acquisition of the system, and I got it from a trustworthy community member. I got home, did some light dusting and fired it up, but POST never kicked in. The PSU fan spins and stays spinning, and the 5153 goes from gray to black as if it's gonna display something...but it never does. The underscore that indicates testing is in progress never appears/ I never hear any beeps, good or bad, and the system just sort of never gets anywhere in general.

    DIP switches are correct for the diagnostic setup and there's nothing obviously awry with the motherboard. Per the MinusZeroDegrees guide I've ruled out a bad PSU and shorts on the system board, rails are all within spec voltage-wise and a PSU substitution didn't change anything. Next culprit's the RAM, but I've reseated everything I can and piggybacked everything I can to no avail. In addition, I've also reseated any and all socketed chips I could find.

    I imagine some Landmark ROMs would be illuminating, but I don't have 'em handy... what's my next step?

  2. #2

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    I would start probing with an oscilloscope to see that voltages look good (e.g. close enough and not too noisy), clock is being provided to the CPU, a correct RESET pulse occurs, address lines are changing, etc.

    Do you have a copy of the Intel iAPX 86, 88 User's Manual ?
    Last edited by Uniballer; September 16th, 2018 at 04:05 AM.

  3. #3
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    Unfortunately, I don't have an oscilloscope - I did verify that the voltages were within spec using my multimeter, but that's about all I can do.

  4. #4
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    Quote Originally Posted by MrArgent View Post
    I imagine some Landmark ROMs would be illuminating, but I don't have 'em handy... what's my next step?
    "Get the Landmark ROMs" would be my suggestion.

  5. #5
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    Aye. Gonna be getting in touch with a friend who'll likely be able to write me some once I have cash spare.

  6. #6

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    Get a $15 POST card and see if you can get a code to go from.

  7. #7
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    The IBM PC line doesn't throw error codes out where a POST card would see them. That was adapted much later. (That said, the Olivetti M24 and possibly a few other 8086-based systems do spit out a few codes on the parallel port as they POST.)
    Offering a bounty for:
    - The software "Overhead Express" (doesn't have to be original, can be a copy)
    - A working Sanyo MBC-775, Olivetti M24, or Logabax 1600
    - Documentation and original disks for: Panasonic Sr. Partner, Zenith Z-160 series
    - Music Construction Set, IBM Music Feature edition (has red sticker on front stating IBM Music Feature)

  8. #8
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    Yup. The parallel card I used to troubleshoot my 6300 and some others a way back won't save me now - I'm gonna pick up a logic probe, get some Landmark ROMs written, and get the 23XX adapter I'll be needing to use them soon. Unfortunately, logic probes are surprisingly difficult to find locally so i'm gonna have to head online for all three.

  9. #9

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    Quote Originally Posted by Trixter View Post
    The IBM PC line doesn't throw error codes out where a POST card would see them. That was adapted much later. (That said, the Olivetti M24 and possibly a few other 8086-based systems do spit out a few codes on the parallel port as they POST.)
    Well damn I did not know that!

  10. #10
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    Logic probe in. Plenty of activity... but i'm not sure how to interpret any of it. DREQ3, DREQ2, and DREQ1 off the 8237 (U35) are floating, and going off the datasheet plus a quick consultation of the technical reference I distinctly suspect that's not supposed to be the case. Waiting on the landmark ROM and adapter now.
    Last edited by MrArgent; September 28th, 2018 at 09:02 PM.

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