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Thread: Adding a Programmer's Console to a PDP-8/a

  1. #21
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    I am working on console #3. This one has a 7408, E10 on the display board with a weak low drive on pin 8. Everything downstream seems to work OK, but I will replace it anyway. It has a bad 74153, E19 on the register board. The replacement should be here next week. There are no outputs from this Mux so you can't enter any number larger than 3. There is a problem with the DISP circuitry where it will only display the contents of the AC. I am debugging that now. The 40 pin ribbon cables that connect the panel to the 8316 had several wire-wrap wires tucked into the connector and had masking tape holding them in place. I suspect that the crimped on connectors were not making good connections so they fixed it by adding wires. I will need to make two more sets of ribbon cables.
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  2. #22
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    The 7475, E26 on the Register board that latches the function button presses doesn't latch. I should have a replacement next week.
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  3. #23
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    With console #1, swapping the two ribbon cables with each other yields very different console behavior.

    I hacked up some 40 pin IDE disk ribbons to replace the defective DEC ribbons and it looks like console #1 is now working OK.
    Last edited by m_thompson; May 1st, 2020 at 05:09 PM.
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  4. #24
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    Using longer front panel cables will let you position the panel on top (or above) the chassis - a big help when you're trouble shooting or working with different ROMs/switch settings.

  5. #25

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    I did exactly that, used a pair of old IDE harddrive cables.

    Good to hear that you got something to work, that makes the rest much easier!

  6. #26
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    Quote Originally Posted by m_thompson View Post
    With console #1, swapping the two ribbon cables with each other yields very different console behavior.

    I hacked up some 40 pin IDE disk ribbons to replace the defective DEC ribbons and it looks like console #1 is now working OK.
    You never check the cables when things are not working? That is among the first things on my list. It's an easy thing to do, and I've had numerous cables with damage over the years...

  7. #27
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    Quote Originally Posted by bqt View Post
    You never check the cables when things are not working?
    I had three different consoles that behaved differently using the same M8316 board and cables, so of course the problem wasn't the cables it was the consoles.
    Next time I will check the cables first.
    Member of the Rhode Island Computer Museum
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  8. #28
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    Console #2
    Has a bad DM8097 E31 on the Register Board. This doesn't let the INIT signal get to the backplane.
    I found a tube of 10x NOS DM8097 DM74367 chips on eBay. They should be here this week.

    The LA and LXA functions don't work, so that is the next project.
    Member of the Rhode Island Computer Museum
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  9. #29
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    Quote Originally Posted by m_thompson View Post
    Console #2
    Has a bad DM8097 E31 on the Register Board. This doesn't let the INIT signal get to the backplane.
    I found a tube of 10x NOS DM8097 DM74367 chips on eBay. They should be here this week.

    The LA and LXA functions don't work, so that is the next project.
    I replaced the DM8097/SN74367 and the second programmer's panel now works OK.

    I am working on the third programmer's panel now, but had to order some more ICs.
    I tested the CPU and core boards from the RICM's 8/a in my 8/a and they work OK. I will make another trip to the warehouse to get the power supply and RX8/E board. We will have to reverse engineer the Brown & Sharpe interface board that is in the 8/a, and then figure out how to talk to the Brown & Sharpe X-Y-Z chassis that are in the cabinet.
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

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