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Thread: TRS-80 Model 4 Power Cable

  1. #1

    Default TRS-80 Model 4 Power Cable

    I am getting a M4 with the power cable cut off. I bought a replacement power cable with Green/white/black wires. The m4 has blue/black/green.

    It looks like the green wire on the M4 is the ground.

    Can anyone confirm how these colors should line up? I am not very electronically adept.



    My Vintage Computer Collection

  2. #2


    With the new cable:
    Green = ground
    White = neutral
    Black = hot

  3. #3
    Join Date
    Mar 2013
    Chaffee, MO


    The Model 4 Schematics don't really show colors of Blue & Black. But, the replacement Power Cable
    has Black = Line (connects to the SMALL blade of Duple Receptacle), White = Neutral (connects to the
    LARGER Blade of Duplex Receptacle) and Green = Ground (connects to round blade of Duplex Receptacle).
    The Line (Black) should also go to the Model 4 Power Supply Terminal that has the FUSE in series on the
    PCB Trace to Power Supply Circuit. Note that Both the Line And Neutral are switched through the Power


  4. #4


    The Vintage Computer Gods giveth and taketh away.

    Thanks for the info above. It got me close enough to take an educated guess and I guessed correctly.

    It booted fine and asked for a diskette. Found a diskette, inserted it, and turned on. SO EAGER!

    Then... POP! FLASH! SMOKE! Burned out something on the diskette drive power supply (see picture). I think there are some youtube videos of repairs for this. I just don't normally get to this level with the snipping and the soldering. Oh well, time to get more proficient in my chosen hobby.

    Thanks again for the help!

    Here is the correct answer:
    M4 Green - Ground
    M4 Brown - Hot
    M4 Blue - Neutral


    Last edited by Kurthamm; April 12th, 2019 at 03:19 PM. Reason: Adding Correct Answer

    My Vintage Computer Collection

  5. #5
    Join Date
    Jun 2010
    Vancouver, BC, Canada


    The reliably explosive RIFA capacitors. Here's a good page on repair:

    My understanding is that you can just safely run with them clipped out. You will bleed noise onto the AC line but I gather that isn't a concern these days as it was back in the 80's.

  6. #6


    i did just remove it so I could keep working. Floppy drive is non-functioning and keyboard has inoperable keys.

    These old 5.25 drives look a lot like the drives I have in my old IBM PC and XTs. Are these compatible?

    I ordered a NEWKEY/80, so that should fix the keyboard.

    Does anyone recondition these keyboards and sell them? I have never had an old M3 or M4 without some keys not working.

    Last edited by Kurthamm; April 13th, 2019 at 03:50 PM. Reason: Add drive info

    My Vintage Computer Collection

  7. #7


    Quote Originally Posted by Kurthamm View Post
    These old 5.25 drives look a lot like the drives I have in my old IBM PC and XTs. Are these compatible?
    Yes, although you have to set the drive select (DS) jumpers to match the drive number (TRS-80s number their drives 0, 1, etc. instead of A, B, etc.).


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