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Thread: Commodore PET 8032-B monitor issue

  1. #1
    Join Date
    Feb 2012
    Location
    Limerick, Ireland
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    148

    Default Commodore PET 8032-B monitor issue

    Hi there
    I got a Commodore PET 8032-B today but the monitor doesn't show anything on the screen.
    It beeps when powered on, beeps when you hold down the space key after a few seconds
    The tube glows on the CRT/
    None of the chips seem to get hot after being left on for a period of time and nothing looks blown on the CRT PCB.
    Any ideas?

  2. #2
    Join Date
    Jan 2012
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    Zurich, Switzerland
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    277

    Default

    I assume you've cranked the brightness adjustment right up? Do you see anything then?

  3. #3
    Join Date
    Feb 2012
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    Limerick, Ireland
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    Default

    Yeah I have, I have turned it both ways, made no difference

  4. #4
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    Feb 2009
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    Default

    The good news is the beeps indicate that a lot of the main board hardware is working. There is 22VAC going to the board from the chassis transformer and a +18VDC regulator on the board. But the tube glow indicates they are probably working to get filament power. What kind of test equipment do you have? Voltmeter, scope?? Do you have the link to the Zimmer schematics for the 8032? Also check/reseat the J7 connector on the main board. This cable takes the video, horizontal drive, and vertical drive TTL signals to the video board.
    -Dave

    Zimmer PET schematics

  5. #5
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    Feb 2012
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    Default

    Thanks Dave
    I'll reseat that cable tomorrow! I'v left the machine at work - I have a standard multimeter, no oscilloscope or anything like that (yet) unfortunately. I don't have any schematics (I'm pretty new to all this so I wouldn't really know what I am looking at to be honest, I only understand the basics of 74LS08N, 74LS86AN etc

  6. #6
    Join Date
    Dec 2005
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    Toronto ON Canada
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    Quote Originally Posted by int 21h View Post
    Thanks Dave
    I'll reseat that cable tomorrow! I'v left the machine at work - I have a standard multimeter, no oscilloscope or anything like that (yet) unfortunately. I don't have any schematics (I'm pretty new to all this so I wouldn't really know what I am looking at to be honest, I only understand the basics of 74LS08N, 74LS86AN etc
    Can you measure the voltages on the six pins of that video connector?

    And don't forget to check the connector at the other end of the video cable, inside the monitor.

  7. #7
    Join Date
    Feb 2012
    Location
    Limerick, Ireland
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    Default

    The connector is fine in both places, I reseated it a while ago just to be sure!
    The voltages are as follows..
    Pin | Voltage
    1 | 20mV
    2 Blank (no pin)
    3 | 3.4V
    4 | 20mV
    5 | 4.7V
    6 | 0.0198V
    7 | 0.15V

    Will check the AC in a while

  8. #8
    Join Date
    Feb 2012
    Location
    Limerick, Ireland
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    Default

    The AC going into the monitor from the transformer is only 7V... which is well below the above specified 22VAC.. Any ideas what could be causing it?

  9. #9
    Join Date
    Feb 2009
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    Default

    Quote Originally Posted by int 21h View Post
    The voltages are as follows..
    Pin | Voltage
    1 | 20mV
    2 Blank (no pin)
    3 | 3.4V
    4 | 20mV
    5 | 4.7V
    6 | 0.0198V
    7 | 0.15V
    Your pinouts are numbered upside down. The key is on pin 6. So that makes: Video = 0.15VDC which does not seem right; I think a mostly blank screen should be > 3.5 VDC, Vertical Drive =4.7 VDC seems a tad high, Horizontal drive = 2.4 VDC is OK. These average DC voltages gives us a good clue on how to proceed. MikeS will know better what the voltages should be.
    -Dave
    Last edited by dave_m; January 9th, 2013 at 10:15 AM.

  10. #10
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    Default

    Quote Originally Posted by int 21h View Post
    The AC going into the monitor from the transformer is only 7V... which is well below the above specified 22VAC.. Any ideas what could be causing it?
    Did you switch the knob on Voltmeter to "AC"?

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