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Thread: PDP11/05 - Quick look and Teardown

  1. #1
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    Default PDP11/05 - Quick look and Teardown

    A quick look inside a DEC PDP11/05, made in Ireland back in about 1973.
    The power supply has some bad electrolytic capacitors, so power on and tryout will have to wait until they have been replaced.

    https://www.youtube.com/watch?v=JA9q6E1sv1I

  2. #2

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    Pretty cool - I noticed the control panel is much smaller than other PDP-11's - can you fully debug with it or is it a smaller more limited control panel?

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    I haven't used it (recently at least, if at all?), so I'm not completely sure.

    But according to the manual (link below), memory contents can be examined and altered, and programs can be single stepped.
    So I'd say it's a go for basic debugging, though without more advanced facilities like breakpoints.

    https://www.vintagecomputer.net/digi...-H05SS-B-D.pdf

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    Quote Originally Posted by intabits View Post
    I haven't used it (recently at least, if at all?), so I'm not completely sure.

    But according to the manual (link below), memory contents can be examined and altered, and programs can be single stepped.
    So I'd say it's a go for basic debugging, though without more advanced facilities like breakpoints.

    https://www.vintagecomputer.net/digi...-H05SS-B-D.pdf
    No front panel operation have things like breakpoints...
    If you want a breakpoint, you insert your HALT where you want it.

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    My question is because usually the CP is taller and has a dial for selecting what is being displayed (so you can evaluate/see things like the registers/accumulator). That seems to be a very compact CP.

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    Quote Originally Posted by bqt View Post
    No front panel operation have things like breakpoints...
    I wouldn't have thought so either, and mentioned it only because the question said "fully debug", and just in case such a beast actually existed.

    Quote Originally Posted by alank2 View Post
    My question is because usually the CP is taller and has a dial for selecting what is being displayed (so you can evaluate/see things like the registers/accumulator). That seems to be a very compact CP.
    Some of the PDP11s have such a switch, I'm not sure if it's present on the majority of models (I suspect not). The /04 & /34 also have just a single display which show address or data depending on context. Some (/03) have no display at all.

    I'm just playing with two PDP8s now. The PDP8/F has the switch, but the 8A is similar to the PDP11/04 & 34. Though it's possibly better than all of them, as it appears to have both address and data displays that are visible simultaneously, unlike any of the other PDPs I have.
    Edit: The 8/F has a separate display for addresses, and the switch selects various data sources to show in the other display, so probably the best of all.
    Last edited by intabits; September 23rd, 2020 at 05:38 AM. Reason: new info

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    That power supply is used in many DEC chassis. We spent a lot of time learning about and repairing one in a DW8-E chassis in a PDP-12. We had to Spice simulate the supply so we could understand how it works. The -15V switcher is very sensitive to the size of the electrolytic capacitors. The one in the PDP-12 has a 3000 uF capacitor, but we found that it would not work correctly with 3000 uF capacitance. Our testing and the simulations showed that it needed more than 3000 uF to work correctly. We are speculating that the +80%/-20% tolerance on the electrolytic almost guaranteed that a capacitor labeled 3000 uF would have more than 3000 uF capacitance and would work correctly.
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

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    Thanks, I'll keep that in mind when I more thoroughly test the caps, and when selecting replacements.

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    Quote Originally Posted by intabits View Post
    Some of the PDP11s have such a switch, I'm not sure if it's present on the majority of models (I suspect not). The /04 & /34 also have just a single display which show address or data depending on context. Some (/03) have no display at all.

    I'm just playing with two PDP8s now. The PDP8/F has the switch, but the 8A is similar to the PDP11/04 & 34. Though it's possibly better than all of them, as it appears to have both address and data displays that are visible simultaneously, unlike any of the other PDPs I have.
    Edit: The 8/F has a separate display for addresses, and the switch selects various data sources to show in the other display, so probably the best of all.
    Unless I remember wrong, the 11/34 is similar to the 8A, in that you actually select what is shown in the data section by manipulating the panel. So there is no rotary switch, but the same functionality is achieved through a different method. In the 8A you have a "DISP" button. So you press one key (they all have labels above telling that they select) and then DISP, and the data part will then display that kind of data. I think 0 is "AC", so 0 DISP will show the AC in the data display. Just as the rotary dial on the 8F set to AC shows the AC.

    The 11/05 is a bit more limited on the front panel, but on the other hand is the CPU rather limited as well. But it can show both address and data on there, and you can examine and modify memory, as well as single step things, so it can pretty much do and show as much as any other front panel. But because of the shared lamps, it is a bit more context about it.

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    I have limited experience with all of these units, but most is with the 11/34 & 04, where I found the lack of simultaneous address & data display annoying, as I was often unsure of which address the data was associated with. It seems the 8/A panel is an improvement on those.

    My home made micros back in the 1970s had both address & data displays, which I miss on my PDP11s.

    My very first computer was an EDUC-8, an Electronics Australia magazine project, which was heavily based on the PDP8. It had LED displays for PC, MA, MB, AC, State & Instruction, so you could see everything. http://www.sworld.com.au/steven/educ-8/index.html

    I wish I had kept the front panels from a couple of System/360s that I scrapped back in the 1980s - Now that was a front Panel!

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