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Thread: TRS-80 Model 3 Upgrades

  1. #1

    Default TRS-80 Model 3 Upgrades

    Hello lovely Tandy folk,
    I recently bought the cassette variant of TRS-80 model 3 for peanuts and plan on putting some money into it.
    It is my understanding that the earlier models that ship without drives also ship without a floppy controller, does that mean external drives also wont work? or are those self contained like a c64 drive?
    I also ran into a lot of conflicting information on differences between the models of trs-80. Some sources say the drives aren't compatible between models (specifically external drives) and other sources say any internal 5.25 DD drive will work with the controller. Would a coco drive be compatible in any way?

    I'm also interested in upgrading to an amber CRT, provided I don't electrocute myself in the process, but it seems like I can only find compatible green tubes.
    Is there something wrong with amber tubes that make them so unused? I always thought they were a little easier on the eyes, but I'm starting to think they have some horrible flaw I'm oblivious to.

    And finally, Ive encountered testimonials from people claiming an 8 inch drive will work in any model of TRS-80 with the standard floppy controller. Has anyone actually done this? It sounds like a horrible idea and I definitely want to try it.

  2. #2
    Join Date
    Mar 2013
    Chaffee, MO


    The Model 3 can be upgraded to a Model 4 if you locate a Model 4 Motherboard. Memory for the Model 3, and Model 4 is getting harder to find.
    It's the 128 Refresh Rate RAM.

    The Model 3 & 4 use a Floppy Disk Controller (FDC) (and RS-232C PCB) that is located behind the Motherboard, and connect to the Motherboard
    with a flexible thin cable. External or Internal Floppy's should work fine on the 3 or 4, as long as your DOS supports them. I've got a good
    Interface Document that covers the Model 1, 3, and 4 with diagrams, pinouts, and information that will help you out.

    The Model 3 Cassette Version doesn't have a 65 Watt Power supply (uses 35 Watt Supply) and you will need another Power Supply to
    help power the various addon's you are installing. The Drive Stands are also missing from the Cassette Version. You can print those
    from the various plans on Thingaverse. You or a buddy will need access to a 3D Printer.

    There is a gent on the VCf that has various parts available for the the TRS-80. It's probably best if you contact him direct with a
    list of things you will need.

    While I haven't tried interfacing a 8" Floppy, you should be able to do it if you get the proper Power Supplies for the 8" Drive.

    Things you will need:
    Drive Stands (used or Printed on 3D Printer)
    2nd Power Supply 65 Watt Astec or Tandy Supply with cables for connections to FDC & RS-232C.
    Assortment of Floppy Drives Full Height or Half height as needed for your specification (Internal or External).
    Flexible cables for FDC & RS-232C Connections.
    Floppy Data Cable (Internal & External) & Power Cables to connect to Floppy Drives.
    DOS - Newdos 80, or whatever you want to use.
    64K RAM w/128 Bit refresh Rate - 8 RAM IC's.
    Replacement RIFA's (Square CAPS on Astec Supplies)

    If I were in your situation, I think I'd get a floppy Drive and get it booting. Then install a Gotek, or HxC Drive
    and after everything was working I'd swap the Drives, so I could still create floppy's in B:

    PM me your email address.

    Last edited by ldkraemer; August 24th, 2018 at 02:28 AM.

  3. #3
    Join Date
    Mar 2016
    Pikesville, Maryland


    I sell parts for the TRS Model 1,3,4,4GA,4D and 4P

    I have just about EVERY PART that goes into any of these machines.

    Good prices also

    Send me PM to discuss your needs further


  4. #4
    Join Date
    Mar 2016
    Pikesville, Maryland


    Other points:

    There is a company that sold amber monochrome monitors but the last time I tried to order one they were "no longer in stock" So you are left with either b/w or green
    Coco drives are usually TEC drives and they ARE comparable.
    You will need the floppy disk controller daughter card and data cable that attaches the controller to the motherboard. You will also need a drive rail kit to install the drives into.
    If you could provide photos of the inside of the computer, folks like us can give you better info on what needs to be done to upgrade your system

    I am retired and this is what I now do - purchase/refurbish/resell Model 1,3,4,4GA,4D and 4P computers. Along with Ian Mavric the two of us can help you out greatly

    See Post #3

  5. #5


    Welp, received the unit today. The CRT was completely destroyed in shipping so I guess that monitor upgrade is essential now.
    I also ordered a 48k parts unit with two floppy drives to steal from, its in pretty poor cosmetic condition so hopefully I can transfer stuff into the 16k model.
    Here is the damage:
    and here is the board:
    and the power supply:

  6. #6


    Quick update: I just realized the connector on the back of the neck is probably done for, and the magnet assembly looks pretty beat up from when the tube imploded. Since i'm going to upgrade the tube anyways, would you happen to have a model 4 display board for sale Jay?

  7. #7
    Join Date
    Mar 2016
    Pikesville, Maryland

    Default Replacement

    I can sell you a COMPLETE replacement CRT assembly - tube, yoke, video board.

    Just swap out the old and insert then new

    If interested please send a message to my email address JAYNEWIRTH@VERIZON.NET to discuss further

  8. #8


    ***puts on moderator hat***

    Please keep posts regarding sales/services to PMs or the appropriate selling/buying forums.


    ***removes moderator hat***

  9. #9


    I had a Model III damaged in shipping - the CRT tore out all four mounting posts on the inside face of the case. It would be a fun project to install a properly sized LCD display, but a CRT will never go back in the case top.

    Proud owner of 80-0007 - The only one of its kind.

  10. #10


    Yea, all but one of mine broke off, but im hopeful that enough Loctite 495 will remedy that.
    If not I guess I can always try to repaint the other shell.

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