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Thread: Model 100 No power up

  1. #21

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    I think it is really hard to sort out AC behavior with a DVM. Ground isn't the best reference in this case. I'd use the emitter as reference.

    M28 pin 13 is.. what voltage?

    The cpu can shut itself down via PCS. Makes debug challenging. Ie... it boots, misreads the ROM, decides to set PCS. Just saying. I've spent hours trying to deloop the power supply.

    I recently thought I had a bad power supply .. it was a bad connection on the main Rom.

  2. #22

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    Quote Originally Posted by Twospruces View Post
    I think it is really hard to sort out AC behavior with a DVM. Ground isn't the best reference in this case. I'd use the emitter as reference.

    M28 pin 13 is.. what voltage?

    The cpu can shut itself down via PCS. Makes debug challenging. Ie... it boots, misreads the ROM, decides to set PCS. Just saying. I've spent hours trying to deloop the power supply.

    I recently thought I had a bad power supply .. it was a bad connection on the main Rom.
    I know this seems like a strange question to ask but have you checked the wall wart you are using to power it?

    The mention of pcs can be avoided by pulling one lead of R123.
    Do you have a bench supply? Something that can go to 6 volts. You'll also need a 100 or so ohm resistor. We can check the feedback regulation of the supply.
    Dwight
    Last edited by Dwight Elvey; November 2nd, 2019 at 08:30 AM.

  3. #23
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    I have an adjustable (brand new) DC power supply. It is set to 6v. I wired it directly to where the negative and positive battery terminals are soldered to the motherboard (thr dc jack I think is broken.. the piece that makes contact with the outside of the barrel is rusted and bent too far away to make contact.

    I can see 6v if I probe the + and - points where the battery terminals are soldered to the board.

  4. #24

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    Here is what I want you to do. Pull the end of D4 at the D13 end ( banded end of D4 )( yes unsolder ).
    Attach a 1K resistor to that D4 end ( tack solder ).
    Attach a 1K ohm resistor to the collector of T13.
    Connect the free end together and to the supply + lead ( crank the voltage down to 4v )
    Put the negative end on the negative side ( ground ) of the PC ( negative side of c83 electorlytic is fine ).
    If things are right, the collector of T13 should be about 1.2V and the banded end of D4 should be 4V.
    Turn the supply to 6V.
    T13 collector should be near 0 to 0.5 volts the banded end of D4 should be 5V.
    All measurements relative to circuit ground.
    I'll be out for the rest of the afternoon ( about 12:50 here now ) so I might not get back until this evening.
    This checks out the feedback circuit.
    Dwight

  5. #25

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    I also have a broken Model 100.
    The motherboard seems to be fine as when I type "beep", it beeps, and I can type something like
    10 beep
    20 goto 10
    and it will beep.
    The screen seems to be completely dead. I used contact cleaner on the display pot and adjusted it, but nothing happened.
    I've tried both the AC adapter and the battery, but neither helped it work.
    Perhaps there is a bad cap?

  6. #26

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    Another suggestion-
    Pull and reseat the M100 Main ROM chip.
    Pull and reseat any RAM modules that are socketed.

    If the power supply is working, but being shutdown erroneously due to poor memory connections, then it might help.
    cheers

  7. #27

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    I should have noted that the external supply was to be with the main power disconnected. It is just to test the zener and transistor.
    Dwight

  8. #28
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    Thanks Dwight et. al. I've been working to remove and where necessary replace components rusted by the aforementioned battery leak. I'll let you know when I get to your experiment Dwight.

    I have tried reseating the RAM and ROM without any effect. If they were/are an issue, could that explain why the voltages at various points surge upwards when I switch the power off? Something isn't holding them down?

    One time, before I changed the caps, I was able to get 5.5V or so at C83.. but I think that might have been an accidental solder bridge or something from my work on the other side of the board.

    One thing I'm wondering about - the board has what I assume is a metallized piece of cardboard that sits in the bottom of the case... the original link didn't seem to have a good connection, so I soldered in another wire and attached it to clean piece of the 'metal'. Didn't make much difference but I wonder how good of a connection it is making.

  9. #29

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    Quote Originally Posted by falter View Post
    Thanks Dwight et. al. I've been working to remove and where necessary replace components rusted by the aforementioned battery leak. I'll let you know when I get to your experiment Dwight.

    I have tried reseating the RAM and ROM without any effect. If they were/are an issue, could that explain why the voltages at various points surge upwards when I switch the power off? Something isn't holding them down?

    One time, before I changed the caps, I was able to get 5.5V or so at C83.. but I think that might have been an accidental solder bridge or something from my work on the other side of the board.

    One thing I'm wondering about - the board has what I assume is a metallized piece of cardboard that sits in the bottom of the case... the original link didn't seem to have a good connection, so I soldered in another wire and attached it to clean piece of the 'metal'. Didn't make much difference but I wonder how good of a connection it is making.
    Such a piece of metal has no function ( except in the Jupitor Ace, needs to have its connection at two places ). It is there for RF shielding. Not RF coming to your machine but to block RF out of you machine. It is not likely to be the problem.
    Dwight

  10. #30
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    Ok. I thought it was ground, because the other side of the 'shield' is conductive, and it has an actual wire bolted to it (green) that runs up to the motherboard and is connected to ground.

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