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Thread: Mark 8 variant

  1. #1

    Default 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 6th, 2014 at 10:51 AM.
    WTB: Case for Altair 8800 ...... Rolands Github projects

  2. #2

    Default

    And a few more pics...

    Mark 8 06.jpg Mark 8 07.jpg

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

  3. #3

    Default

    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

  4. #4

    Default

    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.

    Frank

  5. #5

    Default

    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

  6. #6

    Default

    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

  7. #7

    Default

    Quote 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.

    Frank

  8. #8

    Default

    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

  9. #9

    Default 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 19th, 2014 at 01:47 PM.

  10. #10
    Join Date
    Dec 2011
    Location
    East Coast USA
    Posts
    816

    Default

    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. http://www.willegal.net/scelbi/apps8008.html

    Cheers,
    Corey

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