Author Topic: PDP-11/04 Console Repair - Part 1  (Read 607 times)

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Offline intabits

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PDP-11/04 Console Repair - Part 1
« on: July 16, 2019, 07:49:37 pm »
Continuing with my PDP11/04 and 11/34 repairs, now that the power supplies are sorted,
next comes the console and its interface, the M7859 board (together termed KY11-LB)
These work properly on the 11/34, but there are multiple issues with this section of the 11/04.

Having a working set of interchangeable parts from the 11/34 was a huge help in identifying
where the problems lay in the 11/04. (all three PCBs involved had faults)

I've invested quite some time coming up with a detailed block diagram of the M7859, and then
more time was spent in making an input protection board for a simple logic analyzer.

Block Diagram:-

In this console repair part 1 video I find and repair two problems, both broken conductors,
but realize that the remaining problem(s), even with the aid of the logic analyzer will
need a more rigorous and "clever" approach.

Since recording this, I'm well on the way with my new problem determination design, and I'm
extremely confident that it will locate the fault(s) on the failing M7859 board. I'm still
working on it, and will present it soon in part 2 of the video.

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Offline intabits

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PDP-11/04 Console Repair - Part 1 and 2 of ?...
« Reply #1 on: July 24, 2019, 04:15:52 am »
This is becoming quite a saga!

In this video, I find and fix a fault in the M7859 board (a 74175 Quad D flip-flop), plus uncover and fix a bug in my testing hardware.

But after that, the board is still faulty!
I'm not sure why, as I believe I've tested every part of the board involved with its basic operation when in the computer.

But as the video is already more than long enough, I've ended it at this stage of the troubleshooting, and will have to make a part 3.

And to continue further , my test system needs to be rebuilt, which will take a bit of time.
So when that's done, and I've been able to delve further into the problem, I'll present part 3...


Offline Kean

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Re: PDP-11/04 Console Repair - Part 1
« Reply #2 on: July 24, 2019, 08:59:24 am »
Nice test jig setup & control application
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Offline intabits

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Re: PDP-11/04 Console Repair - Parts 1, 2 and 3
« Reply #3 on: September 29, 2019, 03:27:51 am »
Finally, part 3 of the PDP 11/04 console repair is ready. While I did a lot of work for this, there was also a lot of
procrastination, partly due to getting a pretty tired with this project, and maybe also some fear of not being able to fix it!

In this video, the testing of the M7859 console interface card continues, and now extends to cover almost every part of it.
The testing reveals some strange and hard to explain behavior - can it be fixed?

At the end of the video, I've added a description of the M7859 operation, in a bit more detail than given previously.

The block diagram has also been updated:-


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