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Thread: Model 1 reading 20v on Z2 pin 11. It doesn't seem happy about it.

  1. #31

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    Wire pin 2 more positive, you now have a over current. Before it was showing the Z1 bad ( which may have blown from the over load ). You need to track down the over current.
    If you have a bench supply, you should be able to attach it to the +5 and slowly bring it up. The shorted element should get hot ( not the best way to locate a short ). It is not uncommon for one part to take out others in power supplies.
    I have to look at your ohms readings later when I have more free time to calculate.
    Dwight

  2. #32

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    I will try my FLIR camera first, should I leave Z1 out of its socket for this test?

  3. #33

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    Quote Originally Posted by Towmater View Post
    I will try my FLIR camera first, should I leave Z1 out of its socket for this test?
    Are you going to use a bench 5V supply?
    Dwight

  4. #34

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    I don't have a variable supply, so I will have to inject voltage from various supplies starting from the lowest voltage I have, 1.25V and working up from there. Is there an ideal injection point on the motherboard, something like an easy to clip-to header?

  5. #35
    Join Date
    Mar 2013
    Location
    Chaffee, MO
    Posts
    1,144

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    Towmater,
    Why don't you inject 3 VDC at ~380ma by using two 3.9 OHM resistors in series. That will allow you to chase
    the current path with your voltmeter set for Millivolts. If you are following a PCB trace and the voltage doesn't
    change, there is no current flowing in that PCB trace. Locate a trace that has current flowing down it and the
    lowest voltage reading will be where the short is.

    Larry

  6. #36

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    I'm not sure what the FLIR test has revealed, really... the hottest piece is an empty RAM socket, and a small cap near the big heatsink.
    flir.jpg

  7. #37

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    O' course, injecting voltage made the machine come alive, at least in zombie form.
    behave.jpg

  8. #38
    Join Date
    Mar 2013
    Location
    Chaffee, MO
    Posts
    1,144

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    The hottest piece is an empty RAM socket!
    It would be interesting to remove the IC Socket and look at the traces with a magnifying glass. Then repeat the test.


    Larry

  9. #39

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    I removed the "hot" socket. I upped the injection to 5V, removed Z1, and replaced the Z80 (Again) and have gotten pretty far, I think it is time to strip out the whole +12, -5V components and mod the board for straight 5V? Although this looks like it is doing something, any value entered for men except 65535 and occasionally 16383 is rejected, (but 16383 sometime causes a very long printout of numbers). Entering any basic code line reboots the machine upon hitting enter.
    2018-09-11 22.59.33.jpg
    Last edited by Towmater; September 11th, 2018 at 11:20 PM.

  10. #40

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    I swapped the 4116's for 4164's. I made no modifications to the 4164 chips, I just fed a 5V injection to the 5V and 12V lines, and didn't use the original power supply at all. The Model 1 is now quite alive and hopefully just needs some tweaking of the video circuits to make it less jittery. Otherwise, I'd call this a closed-case, and I'd like to thank all the forum members who helped guide me along the way.
    2018-09-16 20.53.31.jpg

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