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Two In One High Voltage Transformer

By on September 5, 2008

lcd high voltage transformer

If you repair LCD Monitor you must have come across before the high voltage transformer that is located at the inverter board. Normally to drive the top and the bottom backlights/lamps, LCD Monitor designer usually use either one transformer to drive one or two lamp (top and bottom back light) or two transformers to drive the top two lamps and two transformers to drive the two bottom lamps. These designs are very common and could easily be found in most LCD Monitors.

However, since there are many choices for LCD Monitor designers, some prefer to use one transformer to drive 4 backlights! The transformer that you are seeing in the picture actually have two transformers!  One transformer for the two top backlights and one for the the two bottom backlights. So please don’t be mistaken thinking of only one transformer! The most important thing is you must understand the theory of how the LCD Monitor inverter circuit work. Why? Because in the future no matter what kind of inverter designs coming out in the market or what kind of high voltage transformer used, you will still be able to test and repair the unit.



  1. Edward Warbucker

    August 30, 2009 at 8:37 am

    I have a Hanns-G HW173D 17" widescreen LCD monitor I am trying to repair. At first it would not recognize a signal from the VGA cable at all (I do not have access right now to a working card with a DVI port to try that input). I found this guide, , checked out the capacitors mentioned and found them to be bulging, so I replaced them. Now it recognizes the signal fine but the backlight only stays on for about 2 seconds after you turn on the monitor. When the backlight is on everything appears fine--no flickering and the picture looks great. But then it shuts off. I have gone into the on-screen setup menu and made sure that the backlight is turned up. Any ideas?

    I'm not sure if this is the place to post this, but I couldn't find a direct contact listed on the site.

  2. admin

    August 31, 2009 at 4:48 pm

    hi Edward,

    It it shutdown after few seconds then suspect either bad backlight, bad inverter board or even bad main board. After shutdown did you manage to see the dim display?

    If totally dark then make sure the supply voltage to inverter IC still present otherwise suspect a bad Mainboard. If there is supply voltage then check on the back light and components in the inverter board. Sometimes tiny dry joints can be found around the high voltage transformer pin.


  3. Edward Warbucker

    September 1, 2009 at 11:12 am

    Thanks for the tips. I can see still see the display if the room light is good enough. I can see it quite clearly if I shine a flashlight on the screen, so I think it's just the backlight and not the display. The pins on the high-voltage side of the high-voltage transformer are covered in a foam-glue type stuff, I presume for insulation. The small pins on the other side of the transformer appear to be fine. Also, I don't know if it matters, but the backlight will turn on again if I change display modes (like to a different resolution.) In this case it acts just like it does when I first turn the monitor on, going out again after a second or two.

  4. Al Ow

    May 17, 2011 at 7:47 am

    What is the amount of avarage high votlatge for the back light of a LCD monitor?

    Best regards

  5. admin

    May 17, 2011 at 8:57 am

    HI Ai,

    It depends on model usually from 500vac to 1000vac.


  6. Keon

    February 19, 2012 at 10:08 pm

    Hi I also have a Hanns-G HW173D 17″ widescreen monitor. I replace the capcaitors and it worked fine...for 30 minutes or so then the transformer blew out. the yellow one near to 400v capacitor. If anyone can inform me of the name and type of the transformer I could get one with a slightly higher power rating to compensate for the capacitors. Much thanks.

  7. admin

    February 20, 2012 at 9:38 am

    Hi Keon,

    I guess you are referring to the smps transformer. This transformer is unique and hardly could get from the market unless if you have a way to locate the manufactuer or the authorized service center.


  8. med

    February 8, 2017 at 2:35 pm

    Hi i have a power board with one transformer like the picture above the problem is its too noisy is there anyway i cam make it quiet Please ??

    • Jestine Yong

      February 9, 2017 at 6:03 pm

      Hi Med,

      If the power supply is working fine and only have sound you can dip the transformer into shellac for 10 minutes and let it dry for one day. After that fix it and try again and hope the noise will be gone.



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