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Mark 8 variant

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    Mark 8 variant

    Hello everyone,

    I've bought an old Mark 8 computer. The man used the original Mark 8 boards but he built his own version.
    He made all the boards pluggable. And he added some memory cards and designed a video card for it.
    He did not use the LED display but used several 7 segment displays for the read-out. He also made a programming remote.

    I think he did a really nice job back in those days.

    I haven't tested it because I want to readout the EPROM first. There is only one EPROM
    but if this one is distroyed the complete machine will be useless I think.
    So I really hope the EPROM still has his program intact. It's a C8702A version

    Mark 8 01.jpg Mark 8 02.jpg Mark 8 03.jpg Mark 8 04.jpg Mark 8 05.jpg
    Last edited by Roland Huisman; April 6, 2014, 10:51 AM.
    WTB: Case for Altair 8800 ...... Rolands Github projects

    And a few more pics...

    Mark 8 06.jpg Mark 8 07.jpg

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects


      Does anyone have a datasheet of a C8702A EPROM?
      I have no idea how to read this thing. Is it electrically the
      same as an 1702A?

      Thanks in advance for your info!

      Regard, Roland
      WTB: Case for Altair 8800 ...... Rolands Github projects


        Hello Roland,
        yes it is equal to the 1702A.
        I have a reader/programmer for that EPROMs.
        Here is a DIY programmer and here some other info.



          Hello Frank,

          Thanks for your information! I've got the PCB, CPU and instructions
          for the Marting Eberhart programmer. According the website you mentioned,
          the programmer from Martin should support the 8702. But Martin told me he doesn't know...

          Martin asked me for a datasheet to check it. But I can't find it either.
          It should be somewhere I hope...

          Regards, Roland
          WTB: Case for Altair 8800 ...... Rolands Github projects


            I have powered up the Mark 8. First without cards, everytime added
            one single card, checked for heat and measured the power voltages.
            Everything was fine until the mainsfilter blew So I bypassed that one for now.

            I have waited with the eprom. When the Eprom data is saved I will put that one in.

            I assume the Mark 8 should work without the eprom, but it's not for sure.
            I can examine memory and the address counts one up. But I can't write anything in memory.

            Mark 8 08.jpg

            I was wondering, how good is the quality of these wirewrap connections?
            The silver turns black at many wires. Is it wise to solder all these joints?
            Any experiences? The whole backplane is full of wirewrap connections.

            Mark 8 09.jpg

            Regards, Roland
            WTB: Case for Altair 8800 ...... Rolands Github projects


              Originally posted by Roland Huisman View Post
              ...I was wondering, how good is the quality of these wirewrap connections?
              The silver turns black at many wires. Is it wise to solder all these joints?...
              Hello Roland,
              WireWrap connection are generally long lasting.
              The wire what is wrapped round the post is gas tight connected with the post.

              Have you ever try to get solder float on older (black) silver coated wire and the posts? No chance!
              Silver coated wire, which has a massive oxide coating tends to break easily.
              When this already happend with your backplane wraps, i think the best is to rewire it again with wirewrap connections.



                Hello Frank,

                The machine has been stored for about 25 years in a horrible environment.
                The topcover was completely rusted. The wooden panels inside were mildewed.
                And note the huge amount of dirt between the cardholders...

                Mark 8 10.jpg Mark 8 11.jpg Mark 8 12.jpg

                So I began to wonder how the quality might be from the wrapped joints on the connectors.
                When I have placed the eprom back again I can tell more about it's function (I hope...)
                And maybe there are some functions like deposit which would work. But I don't think
                it has anything to do with the eprom.

                I guess there is a tapeloader inside the eprom...

                Regards, Roland
                WTB: Case for Altair 8800 ...... Rolands Github projects


                  Mark 8 is running!

                  Hello Everyone,

                  I've got my Mark 8 up and running. (for so far)

                  The remote was defective. There were only three zeros in the display.
                  I could not put a value into the display. In the meanwhile I've got a lot
                  of the original documentation of this machine. Including the Radio electronics from '74.

                  I began to draw the schematics from the remote. While I was half way I found
                  an NE555 which was used as a clock generator. But no clock signal. After replacing
                  the NE555 I had a clock again. But the panel did still not work.

                  Eventually I ran into a circuit around a 7474 which seems to be broken.
                  After replacing this 7474 the remote came back to live

                  So now I can read and write into each memory location. Still a lot to figure out.

                  Mark 8 13.jpg Mark 8 14.jpg Mark 8 15.jpg Mark 8 16.jpg

                  Defects fixed until now: NE555, 7474, mains noise filter.

                  This machine is inspired by 'the digital group' from Robert Suding.
                  Many (MANY!) original 'the digital group' documents are includes with the machine.
                  The octal input however is completely different than the circuit from 'the digital group'

                  Further, the machine is quite well documented by the brothers Henk and Jaap Berkhoudt
                  who both made this machine in their youth...

                  Regards, Roland
                  Last edited by Roland Huisman; May 19, 2014, 01:47 PM.
                  WTB: Case for Altair 8800 ...... Rolands Github projects


                    Very cool. Welcome to the wonderful world of managing H&L registers by hand...

                    You should be able to use most of Mike Willegal's Scelbi software with minor modification.



                      Hello Corey,

                      Thanks for the link! I have to figure some stuff out. The machine has 14K of memory.
                      So that should give some possibilities

                      And I've got also these books (and more). Games for the 8008.

                      Mark 8 17.jpg

                      The constructor of the computer really enjoyed the
                      pictures of the machine working again for so far.

                      He told me they ran moon lander on the machine once.
                      There is a complete book of scalbi basic with the machine.
                      There are some notes in it because of different I/O addresses.

                      Regards, Roland
                      WTB: Case for Altair 8800 ...... Rolands Github projects


                        Most SCELBI software that I have seen doesn't include I/O drivers. For example the Galaxy program is listed as 4K, but doesn't include any I/O software at all. I had to work pretty hard on tweaking it in order to make it fit in 4K with the added and necessary I/O drivers. A lot of the early/mid 70's home computer gear left a whole a lot to the user to figure out. This is very different than what we are used to with todays canned solutions for everything.

                        If you come up with any additional 8008 software, I'd be more than glad to host it on my 8008 software page.

                        Mike W.


                          Hello Mike,

                          When I have time I will try to sort things out. There are many documents
                          that came with the machine. Probably a nice winter project.

                          An other thing is that my scanner is not supported under windows 8.1... That's also for
                          the winter. Maybe I will buy a new and faster one... Than I can scan the documents.

                          Regards, Roland
                          WTB: Case for Altair 8800 ...... Rolands Github projects


                            Can anyone tell me where I can find little test programs to test a Mark 8?
                            I've wiped the dust off of my Mark8. The last time I had the machine ready
                            to select a memory address and put data into that address.

                            Mark 8 display 123.JPG

                            So now it is time to do a little more testing... I found many big programs
                            and futuristic stuff. But I would like to have a list of basic test programs.

                            Regards, Roland
                            WTB: Case for Altair 8800 ...... Rolands Github projects


                              Hi Roland,

                              Did you ever manage to dump the EPROM in the end?

                              I have been interested in the 8008 for a while. Too much of a faff to make a real one (although people keep tempting me) so I constructed a JavaScript emulator capable of looking like a Scelbi, Mark-8 or MIL MOD-8.

                              I note that you have a few interesting additions to your machine (LED 7-segment displays for instance). Are these described anywhere or were they 'homebrew' by the original constructor do you know?

                              I have just bought myself a little ESP8266 to run the i8008 emulator as a little project whilst in lock-down (although I am working from home and have less free time now than I did before lock-down!).

                              I would be interested in writing a few simple test programs for you if you can pass me details of your I/O capability on the machine.

                              I would also be interested in converting the HexPawn program from the games manual to run on your machine if you would be interested...

                              By the looks of the back panel there is/was a serial port at one time of day. Just thinking of how to get the user to interact with the machine...

                              Any means of saving to tape once you have loaded something by hand?

                              A bit of a distraction me thinks...