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Monitor Proview DX 777NS model 786N-horizontal line

Discussion in 'Troubleshooting and Repair' started by zkostevski, May 31, 2012.

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  1. zkostevski

    zkostevski

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    May 28, 2012

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  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    That's partial "frame collapse". The part of the circuit that generates the voltage to move the electron beam up and down (the "frame" circuitry) is not working properly.
    There are many possible causes, but a likely one is failed electrolytic capacitors in the frame circuit, especially if the monitor is getting old.

    SAFETY ADVICE AND DISCLAIMER

    Before you open the monitor, PLEASE carefully read Sam Goldwasser's safety guidelines at http://www.repairfaq.org/sam/safety.htm

    If you don't have experience working on electronic equipment, you need to follow those safety guidelines very carefully.
    NEVER work on a monitor while it's plugged in. Keep away from the high voltage wire that goes to the bell of the tube. You may need to discharge the main filter capacitor.

    I'm going to suggest how you may be able to fix the monitor, but I can't stand over you and make sure what you're doing is safe, so I can't be held responsible if you get a shock, hurt yourself, or even kill yourself. YOU have to take all possible precautions, and take responsibility for your safety.

    END OF SAFETY ADVICE AND DISCLAIMER

    You can locate the frame circuitry by following the wires from the yoke. The yoke is a large construction with coils of wire inside it, that sits around the neck of the tube in the area where the "bell" of the tube narrows down and becomes the thin neck.
    The yoke normally has four thick wires coming out of it, going to a large 4-way plug that attaches to the main board. Find that connector and look at the tracks under the board to see which direction they go.
    Two of these signals are for horizontal deflection - these go to the line stage, which you can recognise from the horizontal output transformer (flyback transformer) that has the thick insulated wire that goes to the high voltage connection on the bell of the tube.
    The other two signals go to the frame circuit. The frame circuit will have an IC (or maybe some transistors) on a medium-sized heatsink, and a number of large electrolytic capacitors (vertical cylindrical components with a plastic shrunk-on cover, marked with a capacitance value in microfarads (uF or mu-symbol F) and volts).
    Check all these capacitors for obvious signs of deterioration such as bulging, splitting of the vent at the top, leakage of the electrolyte etc. You can get replacements from any electronics component shop. Check under the board for dry joints (solder joints that look crusty or dull or weakened) on all the components in the frame section, and resolder anything suspicious.
    Assuming you don't kill yourself, if this doesn't help you fix the problem, you can try replacing the frame output IC. You may also want to get a schematic diagram for that model, if one is available, and a multimeter for measuring voltages. You can also take some pictures of the top and bottom sides of the main board in the frame section area and upload them here.
    Good luck! And READ THOSE SAFETY GUIDELINES!
     
    Last edited: Jun 8, 2012
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