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Thread: Unique S-100 computer (Z-80/Vector Graphic/Micropolis)

  1. #121

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    Good tip - I'll check that out. However, the cap was on the Bit Streamer board. The system is not booting even without the Bit Streamer installed. Since I do have some (uninitialized) video, wouldn't that point to a problem being on the 12K PROM/RAM or Z80 CPU?
    Last edited by nullvalue; April 30th, 2020 at 08:11 AM.

  2. #122

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    Traced what I hooked up to. The negative end runs to the VEE pin of a 1488P chip. It's carrying -12v.

  3. #123

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    Quote Originally Posted by nullvalue View Post
    Good tip - I'll check that out. However, the cap was on the Bit Streamer board. The system is not booting even without the Bit Streamer installed. Since I do have some (uninitialized) video, wouldn't that point to a problem being on the 12K PROM/RAM or Z80 CPU?
    It really doesn't matter on what board you cause a power supply short if that short, in turn, damages the system power supply. Though with a 7912 in between the short and the system -16v supply, it would not be typical to get past the regulator in a catastrophic way. The short may have damaged the negative supply on another board.

    Measure the system supplies (-16v, +16v, +8v) and see where they are. If they look fine, then look on the boards and check the voltage of any onboard negative supplies and see if they're correct.

    Mike

  4. #124

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    Quote Originally Posted by deramp5113 View Post
    Measure the system supplies (-16v, +16v, +8v) and see where they are. If they look fine, then look on the boards and check the voltage of any onboard negative supplies and see if they're correct.
    I checked the rail voltage and it does not appear that I have a stable -16v on pin 52. I'll check it one moment and it's fine (like -18v) and the next it's gone. Guess I'm going to have to replace the power supply or at least part of it? What's the current best approach for doing this?

  5. #125

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    I was testing voltages with load vs no load. Pulled everything out.. put it all back in and what do you know, system is booting fine now and my -16v rail is back.. bizarre. Will get back to serial testing... lesson learned: don't assume negative end of caps are ground!

    Edit: I think I found my problem with the power supply - may have been nothing to do with my scope hookup afterall. I think my molex connector supplying power to the backplane is lose. I accidentally wiggled it while working in there and the same thing happened where the screen scrambled. This is a relief, I love simple explanations.

    BTW for the serial communications: I did try bumping it up to 9600 baud. Still able to transmit data to the terminal PC, but nothing on the receiving end. (I 06: 00) - will start tracing the signal across the board.
    Last edited by nullvalue; May 1st, 2020 at 06:16 AM.

  6. #126

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    You can quickly check that the input path from the 8251 to the processor is OK by doing an IN 07. Does that give something besides 00?

    Mike

  7. #127

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    Yes it returns "05".

  8. #128

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    So after some further testing, I am able to see the data reach the 1489 receiver chip input (pin 10, Input C) but nothing coming out and nothing reaching the 8251. I'm going to order a replacement for the 1489 and cross my fingers.

  9. #129

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    Quote Originally Posted by deramp5113 View Post
    You can quickly check that the input path from the 8251 to the processor is OK by doing an IN 07. Does that give something besides 00?
    20200509_195530.jpg

    Another problem solved! After replacing the 1489, I am now able to both send and receive data. So.. you had mentioned something about being able to manually send initialization codes?

  10. #130

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    You won’t need to send init codes. The fact that the manual in/out tests work prove that the PROM monitor initialized the port. I’ll update PC2FLOP to allow use of port 6/7 for transfer and then you can try creating a disk. I’ll let you know when it’s posted.

    Mike

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