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

  1. #11

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    Quote Originally Posted by inotarobot View Post
    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
    inotarobot,

    You might try to use an Arduino to read those ROMs.

    Here is a link to a simple Arduino program I made to read an entire 4907 floppy disk controller set of ROMs that were patched by an FPLA I couldn't read:
    https://github.com/mmcgraw74/Tektron...7RomReader.ino

    Monty

  2. #12
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    If you plan to keep an early made machine for ages then it could be worth, after seeking advice on the safest way to open the power supply then carefully inspect it for Dry joints or solder joints that have fine cracking around the through-hole component lead.

    DONT forget to leave it a day or more to discharge and electrical charge the capacitors will retain when you unplug the machine, before attempting to work on the power supplies. Many have very high DC Voltages that can kill when charged

    On this old hand made machine from 1977 to the eye the boards look great. However, using my smartphone on zoom and with correct lightning, I took nearly 100 photos so far.
    Then uploading to my PC and looking at each with the extra zoom I can see the cracks in the solder on a number of boards.
    Thankfully I have plenty reels of lead based resin core solder.



    if you study the pic of a board from this 1977 Signetics 2650 computer and maybe download to your computer and zoom in on the various joint you will clearly see the hairline cracks I refer to. In particular, the pad left mid pic next to the black wire where resistor lead is and ALSO much less obvious the circular crack in the solder on same pad row second from right of the blue lead.

    This is the very reason one takes a lot of care and research.

    My rule is when I get a Very old machine the FIRST thing I do even once its in the car ready to come home is either remove or cut the mains power plug off completely or warp in so much insulation tape that you go "damn yes I cannot succumb to the temptation of just plugging it in and turning it on".

    Second rule I have is ""to get some eggs out of fridge and have them ready as if you plug a machine in and it starts frying then make use of energy to cook some food.""

    Edited foot note: Just kidding re the eggs, BUT i do make sure when I power up an old machine for first time that I have Fire Extinguisher handy, a flre blanket and gloves and a clear exit path to remove machine from my workshop to clear area outside,
    Last edited by inotarobot; July 6th, 2020 at 03:58 AM.

  3. #13
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    Quote Originally Posted by nikola-wan View Post
    inotarobot,

    You might try to use an Arduino to read those ROMs.

    Here is a link to a simple Arduino program I made to read an entire 4907 floppy disk controller set of ROMs that were patched by an FPLA I couldn't read:
    https://github.com/mmcgraw74/Tektron...7RomReader.ino

    Monty
    Thanks Monty, I had a look and will consider this option.

    kind regards
    David

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