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CRT Monitor Display Shrinked At Both Sides

By on May 7, 2008

Dear Jestine,

Thanks for the repair newsletter you’ve sent to me. How are you? Hope you’re having a good day and the business is always in a right track. My dear friend I
want to consult a problem I’ve encountered with my PC monitor, a 14 inch AOC brand model 4Vn. I’ve noticed that the display was shrinked from the both sides
about an inch left and right. I tired to adjust the horizontal function but it is already at maximum adjustment also it can ajust to minimum. I opened it hoping there might be some cold solders only but there is none. What am I gonna do? Where do I start for
troubleshooting? I hope you could help me with this problem. GOD Bless and Thank you very much!


Hi Edwin,
I’m fine here and thank God for all his blessing and His encouragement. In your case, it could be the B+ circuit is not working (not boosting) causing not enough voltage going to the flyback B+ pin thus shrinking the display. Check the filter capacitor, B+ coil, B+ FET, current sense resistor or even a missing gate signal from the h/v oscillator ic. Check also for dry joints in this area too. The B+ fet part number were usually IRF630, IRF640, K1507, K2134 and etc. Hope this helps!

By the way got this email from a subscriber:

Dear Mr.Yong
Thanks for May Newletter,May Almighty God reward you abundantly for all the help you are giving me. I really flying high on the job after i came into contact with you.
Once again thanks.
Stay bless.
Best Regards,



  1. nowdaygood

    May 7, 2008 at 10:29 pm

    Dear jestine
    I know English a little.
    I read this website everyday.Excellent.
    I repair Samsung monitor now.
    B+ too strong.B=50v, B+ = 200v.
    You help me.
    Thanks you.
    Have a best wish.

  2. Jestine

    May 8, 2008 at 2:10 pm

    Please check the gate signal from the h/v oscillator ic to the gate pin of the B+ fet. I came across before a 14" likom monitor where the B+ voltage increased to very high and shutdown the monitor. Tracing backward starting from the b+ fet gate pin lead me to a resistor value where the ohm already increased! The resistor was covered by decayed glue and making the ohm value increased. In your case, it could be a leaky transistor, cap problem or etc. Hope this helps!

  3. Jojo

    November 30, 2010 at 2:39 pm

    Dear Jestine sir

    I am repairing SAMSUNG SYNCMASTER 594 MG,the problem is the B+

    is too high after the FET IRF630, From power supply B+ is 50V,after

    booster circuit it is 200V, please give me a solution.

    Thank You


  4. admin

    November 30, 2010 at 8:48 pm

    Hi Jojo,

    Check the gate signal to the b+ fet. The pulse should have about 10 to 12 volt peak to peak when tested with scope. If you get more than that the B+ output will be increased. Trace the gate signal line to see if there is any bad component and if possible try replace the h/v oscillator ic too.



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