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Thread: H11 (LSI-11) Troubleshooting

  1. #11

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    Ok, more work today:

    o I replaced the three chips relating to the BEVNT signal (two quad opamps and a multivibrator) and the clock signal is now stable but only about 42Hz, not 60. The 7270 is set to ignore the signal anyway.

    o System still exhibits the same random-character problem.

    I'm hoping to get a spare M8043 (DLV11J) and M7270 from a friend of mine to aid in the troubleshooting. At this point I feel that swapping the boards is the only way to narrow it down.

  2. #12

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    Ok, here's an update. I received "test" boards to swap in-and-out of my system and it seems that two things happened to my system when the 12v rail failed a few months ago. Thankfully, the CPU card is fine, but it compromised BOTH SLU cards and the RUN toggle no longer works. So, I will replace the 1488/1489 drivers and UAR/T on both boards and see if that makes a difference. Fixing the RUN should also be somewhat easy since it's only the flip-flop to replace.

    Good projects for a rainy N'oreaster day.

    EDIT: Looks like I might have solved the RUN issue. Still a few other things to iron out. The two old SLUs exhibit the same garbage character issues even after replacing the UAR/T and drivers. Putting them aside for now.
    Last edited by RichCini; October 27th, 2018 at 05:57 PM.

  3. #13

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    Quote Originally Posted by RichCini View Post
    So, I will replace the 1488/1489 drivers and UAR/T on both boards and see if that makes a difference.
    The receiver / transmitter chips are not 1488/1489 but DS9636/9638/9639 8 pin DIL chips on the DLV11-J. I have quite many of these failing on my DLV11-J. Don't really know why. I almost never have problem with the 1488/1489 on other boards.

  4. #14

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    My fault, I should have been clearer in my description. The Heathkit SLUs use a 6402 UAR/T and a 1488/1489 combo. The test card I'm using is the DLV11-J, which works perfectly.

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