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Thread: Commodore pet 3032 screen full of lines

  1. #1

    Default Commodore pet 3032 screen full of lines

    Hi guys,please can anyone help me please?
    I've bought a Cbm 3032 Pet....when i turn on it, i can see only screen full of horizontal lines... (i attach picture)...
    what could cause the problem?
    Thanks!20190911_182458.jpg

  2. #2
    Join Date
    Jun 2012
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    UK - Worcester
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    Of course we can !

    You appear to have horizontal and vertical synchronisation signals (i.e. A full screen raster), but no video signal.

    The brightness looks as though it is turned right up possibly (or this may be a failure mode of the fault).

    The first thing (as usual) is to check if you have any video signal at the connector on the PET main board that connects to the monitor. I can't remember if you have an oscilloscope or not? That would be the best piece of test equipment to use for this.

    No video signal would indicate a fault on the main logic board. The presence of the video signal would indicate a fault on the monitor.

    Divide and conquer!

    Dave

  3. #3

    Default

    Quote Originally Posted by daver2 View Post
    Of course we can !

    You appear to have horizontal and vertical synchronisation signals (i.e. A full screen raster), but no video signal.

    The brightness looks as though it is turned right up possibly (or this may be a failure mode of the fault).

    The first thing (as usual) is to check if you have any video signal at the connector on the PET main board that connects to the monitor. I can't remember if you have an oscilloscope or not? That would be the best piece of test equipment to use for this.

    No video signal would indicate a fault on the main logic board. The presence of the video signal would indicate a fault on the monitor.

    Divide and conquer!

    Dave

    Hello Daver2 how are you??
    Thanks for your answer!
    Unfortunately i don't have scope but i ve a logic probe and multimeter!
    Yes i ve seen that raster's trimmer was to max.....now i see only black screen...

  4. #4
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    Jun 2012
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    Fine thanks, just extremely busy at work...

    Can you measure the dc voltage on J7 pin 1 relative to 0V/GND with your multimeter please. It should be somewhere between 0V and 5V and post the result.

    Dave

  5. #5

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    Quote Originally Posted by daver2 View Post
    fine thanks, just extremely busy at work...

    Can you measure the dc voltage on j7 pin 1 relative to 0v/gnd with your multimeter please. It should be somewhere between 0v and 5v and post the result.

    Dave
    j7 pin 1=4,8 v

  6. #6
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    A voltage reading of 4.8 Volts seems too high to me. The implication being that the video output from the logic board is permanently high.

    Can you detect any pulses (with your logic probe) on J7 pin 1 as a further cross-check?

    The worrying thing is that a video signal level being high should be full white on the monitor (or green for a green screen monitor)...

    I don't think you have two simultaneous faults, but it is possible...

    Let me have a think for other tests that you can easily perform. dave_m might join in as well...

    Dave

  7. #7

    Default

    Quote Originally Posted by daver2 View Post
    A voltage reading of 4.8 Volts seems too high to me. The implication being that the video output from the logic board is permanently high.

    Can you detect any pulses (with your logic probe) on J7 pin 1 as a further cross-check?

    The worrying thing is that a video signal level being high should be full white on the monitor (or green for a green screen monitor)...

    I don't think you have two simultaneous faults, but it is possible...

    Let me have a think for other tests that you can easily perform. dave_m might join in as well...

    Dave

    With logic probe in pin 1 J7 i have always high signal....

  8. #8
    Join Date
    Jun 2012
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    Definitely no video from the main logic board then.

    Not sure (with the signal level being high) why you haven't got a white/green raster...

    Dave

  9. #9

    Default

    Quote Originally Posted by daver2 View Post
    Definitely no video from the main logic board then.

    Not sure (with the signal level being high) why you haven't got a white/green raster...

    Dave


    Today i try to read all roms with eprom programmer, so i can compare with the original files....
    Basic 2??
    Thanks

  10. #10
    Join Date
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    Quote Originally Posted by ilpaninaro View Post

    Today i try to read all roms with eprom programmer, so i can compare with the original files....
    Not needed yet.
    You need to see why no video data. See p.8 of schematic http://www.zimmers.net/anonftp/pub/c...N/320349-8.gif
    Check why G11-pin 6 is stuck high. Check inputs with logic probe: pin 1,2, 4, and 5 of G11 7420 4-input NAND gate. One of those may be stuck low.

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