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Thread: Just got a Signetics 2650 home brew system made 18th August 1977

  1. #1
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    Lightbulb Just got a Signetics 2650 home brew system made 18th August 1977

    Hi all,

    yes, I have been Very quiet posting of late, and my reason a few of you may know, but its water under the bridge.

    Anyways last Tuesday 30th June (2020) I traveled to pick up a Radio Shack TRS-80 that I bought off Gumtree. Mind you I don't really need it, but bought it as a birthday present for myself.

    While there owner, whom I had previously spoken to on phone about my need for 74xx chips, showed me what loose chips he had left, being around 30, so he threw them in

    So packed car and was about to leave when I asked did he have any CGA or EGA monitors. "MM," he says "think there are some in the garden shed", so off we go. Get there and he opens the door. He moves aside an old aluminum box with a keyboard and we look at monitors.

    No, sadly all were VGA.

    So we go to leave shed and I went to put that old box with keyboard back where it had been sitting.

    He said ""don't bother if you want for a few $'s since it was your birthday on the 14th June, put it in your car boot". I really was not sure but we struck a deal and it came home with me.

    This is what looks like from outside. My boot tips will give an idea of the size.



    I lifted the cover and this is my first view of the inside



    I have chatted with him a few times about it since getting it home.

    He had made it himself including laying out and etching a few of the PCBs and he said look at a PCB and you will see my initials followed by a date. I looked and found the date 11th August 1977.

    He was sad as he has only in the last 2 years thinking it was gone, thrown out all his notes and schematics etc, as he had forgotten it was tucked in the garden shed.

    Anyways its going to be a slow and cautious time to get it running.

    All being equal I will post a lot about it over the next x number of days/months, as its going to be a near last to go KEEPER in my collection.

    I am certain many here will get great pleasure seeing the level of Love and Skilled workmanship this old Australian put into building it.

    One of my closest friends has said that is a Stunning save, slight shame the design docs he had were destroyed.

    True it looks very average and ordinary on the outside and could use a clean.. BUT wait there is more to come !!

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    That is fantastic! So this is completely homebrew and not from the 2650 'mini' plans published in Electronics Australia?

    Can't wait to read/see more! Love completely homebrew stuff!!

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    Quote Originally Posted by falter View Post
    That is fantastic! So this is completely homebrew and not from the 2650 'mini' plans published in Electronics Australia?

    Can't wait to read/see more! Love completely homebrew stuff!!
    Hi Falter, the elderly gentleman that made it was a Lab Technician at a Technical College here in Melbourne Australia, and he made it quote "to teach myself about these new things called Computers"

    He had access to equipment at the College as was able to layout (by hand I gather) the PCB circuits, and get the PCB's made.

    All exposed copper tracks are covered with solder, but no solder mask nor silkscreen. Just fine as there is no bare copper to corrode.

    But of all the PCB's ONLY the main 3 Memory Cards 32k in total, are pretty much fully assembled using through-hole 2 layer boards.

    From a conversation a day ago he said he had found the original Signetics 2650 175page book date 1975 that he used along with similar data books. I asked if he used any magazine construction articles and he said No not that he recalled, just used the OEM's data books.

    Never having looked at any Published circuits for 2650 I am taking the gentleman at his word.

    Last edited by inotarobot; July 4th, 2020 at 05:28 PM.

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    The original articles are on the internet archive, it's in Electronics Australia from may '78 though so these boards appear to predate that article. Amazing find, hope you can get it working. 32k of memory is amazing for the time.

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    Quote Originally Posted by bifo86 View Post
    The original articles are on the internet archive, it's in Electronics Australia from may '78 though so these boards appear to predate that article. Amazing find, hope you can get it working. 32k of memory is amazing for the time.
    I am certainly going to take my time and get it running.

    Yes it does predate the EA machine. The old gentleman showed me a few loose boards he had made over the years and I saw he had always used the same ID format on the PCB. Being his Initial (LSO) in Caps followed by two digits of Year then two digits of Month finally adding two digits of Day of Month.
    In this machine the 3 Memory cards have the following near the edge connector LSO 770818 this being date of design ie 18th Aug 1977
    True it was an amazing amount of memory for the time. I have added a photo here of the 3 by 8k Memory Board incase in future any say otherwise

    Last edited by inotarobot; July 5th, 2020 at 03:35 AM.

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    Hopefully, this pic of the rear of a Memory Board will be clear enough to zoom in if any choose



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    By the way, if someone here has 2 of Fairchild 9370 7 seg display drivers with date code around 7540 I would be grateful as out of the 6 on this machine 4 at are good but 2 are bad.

    After some very cautious fault-finding with a multimeter then an HP Logic probe, I choose to swap working for nonworking and fault followed the chip not stayed with socket.

    Important note:- since the Programming panel is unplugable I traced and checked the circuit and was then comfortable to put 5vdc from a current limiting Bench power supply. This unit drew 1.57A at 5v and remained thus for all the live testing. BTW I set the Current Limit at 5amp and had a 3amp fast blow fuse in circuit as a safety.

    one is faulty on one RH upper segment drive
    and the
    other is totally dead

    So far all Displays are fine as are all the 9366 that drive the 9370.

    There is a VERY interesting story about this programming panel that I will share in an up coming posts. Actually a rather spooky story with a happy very happy ending.



    Last edited by inotarobot; July 5th, 2020 at 04:09 AM.

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    Impressive find, hopefully you can get it to run. Does it have any roms, and if so, can you dump them?

    Going by the front switches I'm guessing there might be sockets at the back for a terminal, perhaps?

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    Quote Originally Posted by Robbbert View Post
    Impressive find, hopefully you can get it to run. Does it have any roms, and if so, can you dump them?

    Going by the front switches I'm guessing there might be sockets at the back for a terminal, perhaps?
    Hi Robbbert, Your correct re the front switches

    On top of keyboard at left is these 2 switches


    On top of keyboard at right are these 2 switches


    but no sockets on back


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    Quote Originally Posted by Robbbert View Post
    Impressive find, hopefully, you can get it to run. Does it have any ROMs, and if so, can you dump them ?
    the only rom i can remember seeing is a 4708-6 EPROM with no cover on the window.

    None of my working eprom /rom readers/programmers can do this or 2708 either. i will have to take it somewhere to get read.

    There is an 82S141N on one of the boards, but I have not fully investigated what its doing. However, I suspect it may hold Character lookup table
    Last edited by inotarobot; July 5th, 2020 at 05:39 PM.

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