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Thread: PDP-8L Modules

  1. #1

    Default PDP-8L Modules

    I've acquired an 8L and have begun evaluating its condition.

    Looks fairly complete. Is missing one plastic switch lever but otherwise front panel looks pretty good.

    Did an inventory of the modules and luckily the core memory is present and intact.

    However it is missing the following modules -
    One M220
    One M115
    M706
    M707

    Not sure if the M706 and M707 were optional. I think I could at least start troubleshooting without them?

    The M220 and M115 are a different story. I would need these.

    Anyone have spares (working or not)?

    My first step is reforming power supply caps. So lots of fun ahead!

    Thanks.

  2. #2
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    2,380

    Default

    Firstly, good going on your find!

    You may be able to find someone willing to give/sell you the requisite boards. They do come up on e-bay sometimes - but you will have to be patient.

    Alternatively, look over on http://so-much-stuff.com/pdp8/flipchip/Mxxx.htm and you will find that you may be able to build your own. The M115s look doable. The M220 uses some obsolete chips - so could be more problematic. Vince's M220X seems to be a replica board using PAL/GAL technology to replace the obsolete chips. If you can source the obsolete stuff - go for the 'real' M220B or M22C. If you can't, go for the M220X (but send an e-mail to Vince (or he'll reply here) as he may have the PAL/GAL equations available).

    EDIT: He does! See http://svn.so-much-stuff.com/svn/tru...DEC/Mxxx/M220/ and http://svn.so-much-stuff.com/svn/tru...Mxxx/M220/pld/.

    Some options for you to think about.

    But, you will need to check that the PCB layouts Vince has done are correct yourself...

    Funnily enough, I am doing that for a few of his boards exactly at this moment...

    Dave
    Last edited by daver2; February 2nd, 2019 at 06:35 AM.

  3. #3

    Default

    Congratulations to a nice find!

    Well, I have done a restoration of a PD8/L that was in very bad shape. Here is a write up of the restoration:https://www.pdp-9.net/pdp-8-l

    You may find the module localization chart that I made up useful: http://www.pdp-9.net/docs/pdp-8-l/modules/index.html

    I might have some of the rare IC's (they can be found on Ebay occasionally). Might even have some of the flipchips...

    The M706 and M707 is the Teletype serial interface, you need those as soon as you are ready to load MAINDEC's into the computer. You can easily build a RS232 level converter (I bought one from Vince years ago http://so-much-stuff.com/pdp8/index.php) so you can connect a PC as terminal. There is also a baud rate generator board (M452) replacement that allows you to run at other baud rates that 110 baud (many modern PCs doesn't handle this well, USB adapters not at all without special treatment).

    The 6 x M220 build up all the CPU-registers in the computer (two bits each). You really need to get one of those, but you can test some things before you need one. Well, you can't execute programs without one, but basic deposit and examination of 10 out of 12 bits can be tested anyway (well all of them if you move the M220 around). There must be someone here that sits one. They where just used in PDP-8/L and PDP-8/I (what I know of).

    Good idea to start with the caps! Test the power supply apart from the computer first. And just ask questions and I try to answer them!

  4. #4

    Default

    Quote Originally Posted by anders_bzn View Post
    Congratulations to a nice find!

    Well, I have done a restoration of a PD8/L that was in very bad shape. Here is a write up of the restoration:https://www.pdp-9.net/pdp-8-l
    .....
    Good idea to start with the caps! Test the power supply apart from the computer first. And just ask questions and I try to answer them!
    Amazing restoration job! Thanks for sharing.

    Makes me realize that this is really a daunting task.

    My machine looks to be in somewhat better shape than yours but still a lot of troubleshooting ahead.

    Can't believe you actually repaired your core!

    It may be worthwhile to do some initial continuity checking on my core just to see where I stand.

    It's projects like this that really make me wish I was retired!

  5. #5
    Join Date
    Jul 2014
    Location
    Rhode Island
    Posts
    1,056

    Default

    The RICM made a detailed blog about restoring their 8/L.\
    You can read about it here.
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

  6. #6

    Default

    Depending on what condition your machine is in you might want one like this:



    An M-series module tester.

    Vince Slyngstad makes them based on a design by Warren Stearns. It has built in Raspberry pi.

  7. #7
    Join Date
    Jul 2014
    Location
    Rhode Island
    Posts
    1,056

    Default

    Quote Originally Posted by MattisLind View Post
    Depending on what condition your machine is in you might want one like this:

    An M-series module tester.

    Vince Slyngstad makes them based on a design by Warren Stearns. It has built in Raspberry pi.
    I modified mine to use a USB/SPI cable and wrote Windows software to read the same test files and run the tester.
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

  8. #8

    Default

    Quote Originally Posted by daver2 View Post
    Alternatively, look over on http://so-much-stuff.com/pdp8/flipchip/Mxxx.htm and you will find that you may be able to build your own. The M115s look doable. The M220 uses some obsolete chips - so could be more problematic. Vince's M220X seems to be a replica board using PAL/GAL technology to replace the obsolete chips. If you can source the obsolete stuff - go for the 'real' M220B or M22C. If you can't, go for the M220X (but send an e-mail to Vince (or he'll reply here) as he may have the PAL/GAL equations available).

    EDIT: He does! See http://svn.so-much-stuff.com/svn/tru...DEC/Mxxx/M220/ and http://svn.so-much-stuff.com/svn/tru...Mxxx/M220/pld/.

    Some options for you to think about.
    I actually have boards for the AT1504 version of the M220A/B.

    But, you will need to check that the PCB layouts Vince has done are correct yourself...

    Funnily enough, I am doing that for a few of his boards exactly at this moment...
    Which ones? I may be able to answer that more quickly. Most of the boards have been re-done in the last couple of years to closely match routing of the DEC boards, which also gives them an excellent chance of working (if you can find the vintage parts).

    Vince

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