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Thread: Commodore pet 3032 screen full of lines

  1. #11

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    Quote Originally Posted by dave_m View Post
    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.
    Ok thanks!

    G11:

    Pin 1=high
    Pin 2=pulse
    Pin 4=low
    Pin 5=pulse

  2. #12
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    2,979

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    OK thanks.

    So G11 pin 4 is bad.

    Can you check the following pins for pulsing with your logic probe please:

    G10 pin 6 (74LS00).
    G10 pin 8 (74LS00).

    G9 pins 8 and 9 (74LS74).

    E11 pins 7 and 9 (74LS165).

    Basically, I am working backwards on the schematic diagram until we find where things go from GOOD to BAD...

    Dave

  3. #13

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    Quote Originally Posted by daver2 View Post
    OK thanks.

    So G11 pin 4 is bad.

    Can you check the following pins for pulsing with your logic probe please:

    G10 pin 6 (74LS00).
    G10 pin 8 (74LS00).

    G9 pins 8 and 9 (74LS74).

    E11 pins 7 and 9 (74LS165).

    Basically, I am working backwards on the schematic diagram until we find where things go from GOOD to BAD...

    Dave

    Hello,
    this evening i tried to verify all roms with my eprom programmer and unfortunately, i verified correct only the char rom and edit rom
    The others 3 roms are bad

  4. #14
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    2,979

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    It doesn't matter - you don't have a CRT controller chip on your board (the VDU logic is hardware) so you should still see the 'garbage' screen on start-up.

    Concentrate on that for now and see if we can get a picture...

    Dave

  5. #15

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    Fix one thing at a time, follow what Dave is asking for. You are getting great help. As for the ROMs, they may be different versions or it may be how you are reading them.
    Dwight

  6. #16
    Join Date
    Feb 2009
    Location
    Southern California, USA
    Posts
    2,665

    Default

    Quote Originally Posted by daver2 View Post
    OK thanks.

    So G11 pin 4 is bad.

    Can you check the following pins for pulsing with your logic probe please:

    G10 pin 6 (74LS00).
    G10 pin 8 (74LS00).

    G9 pins 8 and 9 (74LS74).

    E11 pins 7 and 9 (74LS165).

    Basically, I am working backwards on the schematic diagram until we find where things go from GOOD to BAD...

    Dave
    Right daver2! This may be a quick fix. It should be one of those signals.

  7. #17

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    The area that Dave is looking at is a to create inverted video. It could be stuck in one position.
    My bet is with the E11 side of things but without data back, that is just a unfounded guess.
    Dwight

  8. #18
    Join Date
    Feb 2009
    Location
    Southern California, USA
    Posts
    2,665

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    Quote Originally Posted by Dwight Elvey View Post
    My bet is with the E11 side of things but without data back, that is just a unfounded guess.
    There aren't too many chips it can be: the E11 Shift Register, the G9 Flip Flop, or the G10 and H10 NAND gates. E11 is the most complicated part so your guess may be correct. Five minutes with a scope and we would have this thing fixed (as far as a video signal). Our Paninero will find it.

  9. #19

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    Sorry but i think that problem in this pet are the Rom....
    I tried to insert Pet tester in ud9 with only char rom inserted and i can see this double 20190913_170032.jpg20190913_170034.jpgscreen:

  10. #20

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    Quote Originally Posted by daver2 View Post
    OK thanks.

    So G11 pin 4 is bad.

    Can you check the following pins for pulsing with your logic probe please:

    G10 pin 6 (74LS00).
    G10 pin 8 (74LS00).

    G9 pins 8 and 9 (74LS74).

    E11 pins 7 and 9 (74LS165).

    Basically, I am working backwards on the schematic diagram until we find where things go from GOOD to BAD...

    Dave
    For this test
    should I leave all ROMs inserted?

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