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Thread: Help, I am lookin for a modifacation for my model 1 system

  1. #1

    Default Help, I am lookin for a modifacation for my model 1 system

    Hi Guys,
    a friend gave me his old EI with 0k of memory, he had modified his keyboard to use 64k memory.
    I want to add memory to the EI now is there anything I need to undo?

    Also is there any place that has a knowledge base of various mods for the Model 1?


  2. #2
    Join Date
    Mar 2013
    Chaffee, MO


    Your best bet is to keep the 64K RAM IC's in the Keyboard and not add any memory to the
    EI. The 64K RAM is a lit better than the Older RAM that used the -5VDC on one pin.
    Those are prone to internal shorting and getting HOT.

    The Model 1 Modifications I used were:
    1. Third Party Lower Case Modification.
    Depending on your Character Generator's Number, you may be able to easily
    get the Lower Case Characters.
    I simplified it this way which has served me well since the 80s.

    If your character generator (Z29) last 4 numbers are 3001 or 6670, then you do the mod Lowercase with Upper from Custom TRS-80

    If your character generator last for numbers are 6673 or 6674, then you do the Radio Shack lowercase mod, from the same book.

    All other LC mods are complicated or unnecessary in this day and age, and in fact when I buy systems with other mods I undo
    them and set them up as listed, above.

    For the record:
    3001 : early systems, lowercase but no descenders, and a flying 'a' due to Motorola manufacturing fault (so they sold these
    chips cheap to RS who figured they didn't need LC anyway)
    6670 : mid-production systems, same as above but with no flying 'a'
    6673 : late systems, custom part made especially for the M1 for Radio Shack and included with most late 79 and 1980 machines.
    By this time RS was selling the LC modification "kit" for $99 but if the computer already had the 6673 then the 1-min job
    was to cut the trace, install the stacked 2102s into the already fitted socket, and solder two wires. It probably took
    longer for the soldering iron to warm up than to make the mod.

    2. Upgrade ROM from Ver 1.1 to 1.3 (3 Chip Set).
    This is easy to do, and well documented. It gets rid if the Key Bounce, and the critical
    timing issue when using cassette tape for storage and retrieval. There may be other
    things that were corrected, but I'm not remembering them these days. (I have a document
    on exactly what was done to get Ver 1.3 ROMS installed.)
    PM me your email address, and request Model 1 1.3 ROM DOC, if you are interested.

    3. I also added the AeroComp Double Density Modification, and used 3 AeroComp Flippy Drives.
    I used NEWDOS 80 with the first Floppy having a Single Density Boot Track.

    About the best place to locate the mods were the Books by Dennis Kitsz, and others for customizing the
    Computers. I've got a few PDF's and a couple printed books.
    Custom_TRS-80_and_Other_Mysteries_1982_Dennis_Bathory_Kitsz.p df
    TRS-80_Disk_and_Other_Mysteries_1980_Harvard_C._Pennin gton.pdf

    Last edited by ldkraemer; January 15th, 2021 at 02:56 AM.

  3. #3


    Hi Larry, unfortunately I do not have his keyboard unit that's why I was trying to undo his mod.

    Thanks for the other great info.


  4. #4
    Join Date
    Mar 2013
    Chaffee, MO


    So, you are going to use a stock Model 1 keyboard, and the EI that has zero memory installed.
    If so, then all you need to do is add the two banks of 16K RAM to the EI. You will need two
    of the Brick Power Supplies and the proper cable(s) from the EI to the Model 1. There were three
    versions of cables to interface with two units. If the EI has no additional cables protruding, a standard
    cable from Keyboard to EI should get you going.

    If your keyboard doesn't have more memory than 16K, it would probably be cheapest and BEST to
    purchase the 64K RAM IC's (128 Bit Refresh Rate--NOT 256) and install them in the Keyboard.

    I've got a document that details that modification. (That will prevent the noise and clocking problems
    some EI's had between the Keyboard Unit and the EI.)

    I was lucky not to have those type problems.

    Last edited by ldkraemer; January 15th, 2021 at 06:40 AM.

  5. #5


    Quote Originally Posted by ldkraemer View Post
    (128 Bit Refresh Rate--NOT 256)
    My brain hurts now. Is it easy to mod the keyboard for 64K?

  6. #6
    Join Date
    Mar 2013
    Chaffee, MO


    Yes, it is easy. PM me your email address and I'll send you the Document.



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