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Thread: TRS-80 Model 1 Power Supply - not working

  1. #1

    Default TRS-80 Model 1 Power Supply - not working

    Hi gang,

    Just added my high school computer to my vintage collection - system and monitor. Monitor powers on, but power supply - no red light on system.

    Cut open the case - fuse looked ok, but replaced. Nothing looks blown or burnt, so ... how can you test (voltmeter, etc) that this thing is sending power, AND, if dead, where can you find one ?

    Thanks all !

  2. #2
    Join Date
    Jun 2015
    Location
    Sioux Falls SD
    Posts
    366

    Default

    Get a copy of the Technical Reference Manual and start at the power supply section. You can check for voltages at the CPU connector. The regulation is done inside the keyboard unit.

    https://archive.org/details/TRS-80_M...82_Radio_Shack

  3. #3

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    Quote Originally Posted by lafos View Post
    Get a copy of the Technical Reference Manual and start at the power supply section. You can check for voltages at the CPU connector. The regulation is done inside the keyboard unit.

    https://archive.org/details/TRS-80_M...82_Radio_Shack
    ...

    Thanks - but I am not an elec. engineer - and did simple pin checking and didn't get much of a readout

  4. #4

    Default TRS-80 Model 1 Power Supply - not working

    Hello, If your technical expertise is limited to basic electronics your best bet is of course looking on Ebay for a replacement power supply. They can go for around $50.00 or so. To check the pinouts of the existing power supply go to http://www.trs-80.com/wordpress/zaps...-power-supply/.

    > Charles

  5. #5

    Default

    Dawsoca - thanks. I could probably replace all the components in the power supply, but short of that, if I am not getting the right power from pins 1 and 5, or 2 and 3 (I think), then thats where I get stuck. Troubleshooting which component (and there are not many) is the issue.

  6. #6

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    Hello pkasson - umm... the pins you need to check are 1 - 3 for AC Voltage and then 2 - 4 for DC Voltage I think. The Pin 5 is not connected to anything. The only components in the Power Transformer are the Transformer, Diode, Fuse and DIN cable. After checking the DIN connector pins for proper voltage you could unplug the power supply and check for continuity using the resistor function of your volt meter as there could be a break in the cable or DIN connector back-side.

    If you don't feel comfortable messing with this your best bet is Ebay. There are two TRS-80 Power supply transformers on sale there for about $75.00 and yes, that is expensive.

    good luck;
    > Charles

  7. #7

    Default

    Dawscoa - thanks again. I will check the pins again, I think I got some reading for 1 and 3, but nothing for 2 and 4, if I setup my volt meter up correctly. If I am getting nothing for 2 and 4, then the secondary is not working ?

    Like you said, and from what I can see and read, there is not much to this, so if 2 and 4 is getting nothing, then it sounds like the transformer process is not working ? Meaning, from what I understand and I am not an EE, there is no direct connection between AC and DC and that the windings between the two is how DC power is created ?

  8. #8
    Join Date
    Mar 2016
    Location
    Pikesville, Maryland
    Posts
    216

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    I can sell you one for $25 (I have several of them in my inventory) - Don't buy the ones on ebay - OVERPRICED !!!!

    send me an email at jaynewirth@verizon.net if you are interested.

  9. #9

    Default

    Hi
    It isn't clear as to if it is his transformer or the regulator?
    Dwight

  10. #10

    Default

    Ok Jay ... I will drop you a line.

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