How To Completely Test LCD Inverter Transformer

By on January 5, 2015
lcd tv transformer test

 

 

 

 

 

 

 

 

 

The function of LCD TV/Monitor high voltage transformer is to produce high AC voltage (from few hundreds to more than a thousand AC volt) to light up the CCFL backlight. If this transformer have problem it will cause the LCD screen to light up for a second and then shutdown or to have dim display problem.  Basically the high voltage transformer can have four types of problems such as:

1)      Open circuit especially the secondary winding

2)      Shorted in secondary winding

3)      Increase in resistance in secondary winding

4)      Breakdown when under load

Note: The primary winding seems to be quite robust and rarely give problem.

 

How are we going to know if the high voltage transformer have problem or not?  The answer for it is to use the right test equipment to check it.

1)      Open circuit especially the secondary winding

All secondary winding should have resistance between several hundred to several thousand Ohms. Just place your Ohmmeter at the secondary pins and you should get the Ohm reading. If you did not get any reading means the secondary winding already open circuit.

inverter transformer testings

An open secondary winding can cause display to shutdown in few seconds or dim display depending on how many transformer is used in the circuit design.  This means if the circuit design is only using one high voltage transformer to support one backlight and if the secondary winding is open circuit then there will be dim display problem.  If it is uses two transformers and one of the transformers secondary winding has an open circuit then the symptom would be display shutting down in a second or two.

 

Note: Primary winding also has resistance and the Ohm value is very small.

 

2)      Shorted in secondary winding

If there is a shorted secondary winding, a normal multimeter would not be able to detect it. You need to use a coil tester such as the Blue Ring Tester.  For a much bigger high voltage transformer you can expect at least 4 LEDs will light up.  If the tester did not light up at all means the secondary winding is shorted.

inverter transformer testing

Note: You also have to take note that a slighlty small high voltage transformer secondary winding may not be able to read by the Blue Ring Tester.  The tester could read up until 2 or 3 LED lights only. However, if the LCD inverter has more than one high voltage transformer then it would be easy to judge the result (comparison test).

lcd monitor transformer testingsYou can use the comparison method on the two transformers and locate the faulty one

lcd monitor transformer testing

Some designs only have one transformer but you still can compare the winding because the above transformer have one primary winding and two secondary windings

 

3)      Increase in resistance in secondary winding

You will be surprised that the resistance in secondary can increase when there is a problem. It is due to a prolong increasing in temperature in the high voltage transformer.

lcd monitor transformer test

lcd monitor transformer testsIf you notice a vast different in Ohm’s reading (usually higher resistance) meaning to say  the transformer is bad.

I have found many LCD high voltage transformers problem are due to increase in resistance in secondary winding in one of the transformers.

Note:  A slight different in resistance reading is acceptable when checking on two similar transformers.

Most of the LCD inverter boards have more than one high voltage transformer thus it would be easy to compare the secondary winding and find out the problematic one.

4)      Breakdown when under load

Although is rare, I did came across one before. On top of the secondary winding I saw a very tiny spark while the LCD Monitor inverter was working. It caused intermittent display shutdown. When I took out the transformer and test it, it seems to be working fine. A replacement brought the LCD Monitor back to life again.

lcd tv transformer testings

The question now, what if the transformer is fully covered and you can’t see the spark. In this case, it would be a little bit tough to solve it. What you can do is to make sure there is no bad components in the inverter circuit and all the CCFL lights are good (you can test them with a CCFL backlight tester). Check the transformer for good resistance reading and make sure no shorted reading (test it with a Blue Ring Tester). This means if you have checked all the parts and the LCD Monitor or the TV still have intermittent display shutdown problem then there is a possibility one of the high voltage transformers could be breaking down when under load.

Conclusion- I hope the above article will help you in solving LCD problem that is related to the inverter high voltage transformer. If you have additional method in testing/checking of the high voltage transformer please do leave your comment below-thanks.

jestineyongpowersupply

 

 

 

 

 

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96 Comments

  1. RACHID

    October 7, 2017 at 6:13 am

    Thanks alot Mr JESTINE, this article helped me so much. I will stay in touch

    Likes(1)Dislikes(0)
    • Jestine Yong

      October 7, 2017 at 9:46 am

      Hi Rachid,

      You are welcome.

      Jestine

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      • RACHID

        October 13, 2017 at 11:42 am

        Hi Jestine!

        I have an LG lcd tv lg27lz5rv-zc no picture no sound, green light LED stays ON, Power BD OK (all voltages ok) I suspect 1 or 2 transformers on the inverter board MODEL darfon V070 to be faulty.
        my question is apart of the blue ring and the ohm-meter test can I test the inverter board without connecting the bulb lamp to the suspect transformer or should I simply desolder the transformer sort of bypassing for test .
        I have an average level ..

        Thanks in advance.

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        • Jestine Yong

          October 16, 2017 at 11:08 am

          Hi Rachid,

          If you remove the backlight or one of the transformer the Tv will shutdown and you can't perform the actual test. In your case, have you checked if there DC supply to the Inverter IC? The best is to test the backlight with LCD backlight tester and remove the transformer and compare with each others using ohm and ring tester.

          Jestine.

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  2. RACHID

    October 17, 2017 at 10:56 am

    Hi Jestine,

    Thanks for responding back;
    all voltages are ok going to inverter board and ic
    I suspect 1 or 2 transforms to be faulty (Using ohm meter measure) and I want to bypass it by disabling the sense line in the feedback of the second secondary winding of the faulty transformer (saw that in youtube) but I am not sure I get it and my board is a bit different

    my inverter board is actually like this one: http://www.ebay.com/itm/Inverter-board-Darfon-V070-48-V0708-001-E206453-V070-001-/272592753166

    is there any way to bypass the transformer without having to change it????

    Thank you for your help,
    Rachid.

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    • Jestine Yong

      October 17, 2017 at 9:09 pm

      Hi Rachid,
      I suggest that you visit the link below to get some ideas:

      http://www.bestelectronicarticles.com/consumer-electronics/lcd-televisions/how-to-bypass-lcd-tv-inverter-board-shutdown-backlight-system.html

      Jestine

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  3. RACHID

    October 19, 2017 at 9:16 am

    Hi Jestine,
    Yes that article was realy helpful;
    I will gave it a try and I will be carefull,
    Thanks a lot my friend,
    I wish you all the best ...

    Rachid IBOUZIR

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  4. Michael Rowley

    October 23, 2017 at 5:56 pm

    Hi, I have 2 6131020001p00 Transformers on my dell monitor, I have purchased the Monitors to make a Digital photo frame. They have a 240v transformer built inside which I wish to remove and just use the video board and the transformer board for the lcd so I can operate them from a seperate DC input. What voltage do the LCD light Transformers operate at on the input side? Many Thanks.

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    • Jestine Yong

      October 24, 2017 at 11:51 am

      Hi Michael,
      The function of the power supply board that consist of power transformer is to supply DC voltages to the mainboard and inverter board. Usually for LCD Monitors it has two output voltages which is the 5 volt and 12 to 19 vdc (depending on the brand and model). The 5 volt is to supply to the mainboard while the 12 to 19 volt is supply to the inverter board. The inverter board would not work if it did not get a signal from the mainboard. The inverter transformer will take in the 12 to 19 volt with the pulse signal generated by the inverter IC will produce about 500 to more than 1000 vac. You need to open the LCD Monitor and check what are the dc output voltages from the power supply before you can use a separate one or two DC input to power up the mianboard and the inverter board.

      Jestine

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  5. abigail karonga

    October 26, 2017 at 9:43 pm

    Thank you Mr Jestine I want to become a professional electronic repairer am reading theory books but its Still like rocket science to me hopefully with your articles like this will achieve my dream because of step by step clarity as well as clear visual impression from high resolution pictures thanks a lot

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  6. Alade Oladosu

    October 30, 2017 at 7:18 pm

    I have a samsung lcd tv LA32D450 the inverter board is bad no output voltage to the ccfl
    The inverter board number is CM32T_BHS

    Likes(0)Dislikes(0)
    • Jestine Yong

      October 30, 2017 at 9:35 pm

      Hi Alade,

      What have you checked?

      Jestine

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