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? Fixing Vertical Deflection Problem on Old Screen

Discussion in 'Electronic Repair' started by [email protected], Jun 29, 2007.

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  1. Guest

    Hi,

    I've got an old Commodore monitor that's been having some problems for
    the past several months. Sometimes it's fine but more and more often,
    the picture shrinks to a few lines in the middle of the screen.

    These past two weeks have pretty much confirmed what the problem is
    since last Monday (when it was hotter than Hell), it worked fine for a
    few days but stopped during the weekend (when it cooled down a lot),
    and then the same pattern repeated this week.

    Obviously the vertical deflection circuit has developed a problem,
    either a bad (thermo-sensitive) capacitor, or perhaps just a loose
    connection (solder joint).

    I haven't cracked it open since figuring out what the problem likely
    is, but I hope to finally fix it this weekend. I just don't know what
    to look for in this old thing. I am hoping that someone can advise me
    of what to look for and an effective technique for pinpointing the
    problem area. Pictures are more than welcome. In fact, I will try to
    take a photo of the area and post it.


    Thanks a lot.
     
  2. Guest

  3. The vertical deflection is not on the CRT board, it's on the main board.
    It might be marked "VERTICAL", "VERT", etc.
    THere should be an IC and several small capacitors. Replace the caps,
    resolder the ICs, everything should be fine.
    I can't tell for sure but the IC mounted to a heat sink under the front
    of the Yoke could be it.
     
  4. Sounds like cracked solder joints on the mainboard. Trace the 4 wire
    cable from the deflection yoke to the mainboard connector. It may even
    be right there.

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  5. Franc Zabkar

    Franc Zabkar Guest

    There are four wires going to the yoke. Two will be for the
    horizontal, and the other two for the vertical. Follow them back to
    the PCB. The thicker (?) wires are probably the horizontal.

    - Franc Zabkar
     
  6. n/a

    n/a Guest

    Thanks for the tips Sam and Franc. There is a four-wire connector
    that goes from the yoke to the board. The red wire is the thickest,
    and the other three are the same.

    I traced it on the PCB and looked around but could not find an obvious
    bad joint. I poked a bit at the board and the various connections in
    the area with a rubber pointer and it occasionally did work for a
    moment, but I was unable to identify one concretely.

    Here's a shot of the area. The connector is the vertical strip just
    to the right of center, next to the box (the first three are the thin
    wires, the fourth is not connected, and the bottom is the thick red).
    I could not find any labels identifying the vertical deflection, or
    any ICs or caps in the area.

    I should also point out that there seems to be a lot of yellow, crusty
    materials on and around the board. Some of the components seem to be
    glued in place by some yucky old-and hardened-gunk (almost like it has
    leaked out from the bottom), and there are other splotches on various
    places. Some of it may be residual flux, but others are not. I
    considered cleaning some of it, but decided against it for now.


    I also called around town and there was only one place that said they
    could/would fix it, but it would cost a ridiculous amount. I'm going
    to end up having to fix it myself because I can't afford to have
    someone fix it, and I don't want to just replace it (assuming that I
    could afford to) because it's an authentic C64 monitor for an
    authentic C64-assuming that I can find the console, disk drive, etc.
    in the basement.
     
  7. n/a

    n/a Guest

    The vertical deflection is not on the CRT board, it's on the main board.

    Thanks for the tips everyone. There is a four-wire connector
    that goes from the yoke to the board. The red wire is the thickest,
    and the other three are the same.

    I traced it on the PCB and looked around but could not find an
    obvious
    bad joint. I poked a bit at the board and the various connections in
    the area with a rubber pointer and it occasionally did work for a
    moment, but I was unable to identify one concretely.


    Here's a shot of the area. The connector is the vertical strip just
    to the right of center, next to the box (the first three are the thin
    wires, the fourth is not connected, and the bottom is the thick red).
    I could not find any labels identifying the vertical deflection, or
    any ICs or caps in the area.


    I should also point out that there seems to be a lot of yellow,
    crusty
    materials on and around the board. Some of the components seem to be
    glued in place by some yucky old-and hardened-gunk (almost like it
    has
    leaked out from the bottom), and there are other splotches on various
    places. Some of it may be residual flux, but others are not. I
    considered cleaning some of it, but decided against it for now.


    I also called around town and there was only one place that said they
    could/would fix it, but it would cost a ridiculous amount. I'm going
    to end up having to fix it myself because I can't afford to have
    someone fix it, and I don't want to just replace it (assuming that I
    could afford to) because it's an authentic C64 monitor for an
    authentic C64-assuming that I can find the console, disk drive, etc.
    in the basement.
     
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