How To Completely Test LCD Inverter Transformer
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.
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.
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).
You can use the comparison method on the two transformers and locate the faulty one
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.
If 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.
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.
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Leave a Reply
RACHID
October 7, 2017 at 6:13 am
Thanks alot Mr JESTINE, this article helped me so much. I will stay in touch
Jestine Yong
October 7, 2017 at 9:46 am
Hi Rachid,
You are welcome.
Jestine
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.
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.
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.
Jestine Yong
October 17, 2017 at 9:09 pm
Hi Rachid,
I suggest that you visit the link below to get some ideas:
https://www.jestineyong.com/consumer-electronics/lcd-televisions/how-to-bypass-lcd-tv-inverter-board-shutdown-backlight-system.html
Jestine
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
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.
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
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
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
Jestine Yong
October 30, 2017 at 9:35 pm
Hi Alade,
What have you checked?
Jestine
haseebraza
November 29, 2017 at 4:02 am
nice work friends
Dp
January 18, 2018 at 2:16 pm
Hi. I have Samsung scanemaster 540n
Lcd monitor the problem is backlight
After power on the Lcd backlight stop in 2 seconds please give me Solutions
Aziz
February 12, 2018 at 2:15 pm
Hi mr. Jestine yong thank you very much for your e-mail. I'm from afghanistan
Jestine Yong
February 12, 2018 at 5:37 pm
Hi Aziz,
You can visit this link to post your message :
https://jestineyong.com/contact-me/
Jestine
Ted
February 15, 2018 at 5:19 am
Thanks to this article, I was able to find the problem on my old lcd monitor, and fix it. Thank you.
Shah Muhammad
April 23, 2018 at 5:12 am
Hi Jestine!
i have a haier lcd tv LE32B50.I am sure you can help in this regard that by power on it does not on blue light comes on but after few seconds red liht comes on and backlight comes on but fails to on continuous .By disconnecting baccklight connectors blue light stays on and after this reconnecting connectors backlight comes on and lcd performs all ok but after power off the same problem is faced.All voltages are ok during power on problem.Please help me to fix this .
Jestine Yong
April 30, 2018 at 8:58 am
Hi Shah,
Have you checked that all the Dc voltages to the mainboard are good? If good then probably is the firmware fault. Without hands on assessment on the set it would be hard for me to tell you what will be the exact problem of your tv.
Jestine
ugo
April 29, 2018 at 2:53 pm
Hi Jestine, I have Philips TV that breaks down when under load. I change the inverter transformer and it worked for a while and the same problem started again (breaking down when under load). what could be causing this even though I have change the transformer twice now and same thing happens each time I change it. please I need an urgent reply,my design has only one transformer. thanks
Jestine Yong
May 2, 2018 at 10:42 am
Hi Ugo,
Can you elaborate what do you mean by TV breakdown under load? Your power breakdown and LED did not lighted up? Your display shutdown? Why do you change the inverter transformer? Is it shorted? Is it burnt?
Jestine
ulises aguilar pazzani
April 17, 2020 at 12:17 pm
Mr Yong grate information
Ulises Aguilar
July 25, 2020 at 2:59 am
Mr yong great info
Parasuraman S
September 17, 2021 at 8:10 am
Very, very useful information on troubleshooting! Many thanks for sharing!
Jestine Yong
September 17, 2021 at 12:06 pm
Hi Parasuraman,
You are welcome.
Jestine
Andrea Del Corso
October 8, 2021 at 9:47 pm
Ottimo lavoro di divulgazione.Complimenti!
===============================
Great dissemination work. Congratulations!
Jestine Yong
October 11, 2021 at 7:28 pm
Hi Andrea,
You are welcome.
Jestine
Gerard
October 12, 2021 at 7:01 am
Hi,
Thanks for this info - very helpful. The last picture in this article shows a transformer that looks very similar, if not the same, core/bobbin as in my monitor, and one of the transformers in that has gone open circuit. I'm trying to find a drop in replacement. The turns ratio is 9:2400 with a secondary resistance of around 1.1k. Would you know of any suitable part numbers to source, or can you recall the part number of that transformer in the last image?
thanks
Gerard
Jestine Yong
October 14, 2021 at 3:47 pm
Hi Gerard,
I have the board with me and I did took out the transformer and there was no part number written on it and the secondary winding was about 750 Ohm. Sorry I do not have info of where to source for this kind of transformer.
Jestine
Anton
November 16, 2022 at 7:36 am
Hello Jestine,
I was searching the internet for a solution to my problem and I think this is the place to find it.
We are not very knowledgeable regarding these procedures but we are willing to learn and try to fix them, be patient.
My UHD TV had dim light, and the picture on the screen is barely visible only if it is completely dark in the room. Changing the brightness setting to a different value has no effect. I notice there is a buzzing sound coming from the back so I opened the case and localized it. It seems to me that the buzzing noise is coming from a piece that looks like a transformer.
I would like to know if this is a possible fix.
Thank you.
Jestine Yong
November 24, 2022 at 4:09 pm
Hi Anton,
A dim display could indicate the LED backlight did not get enough DC voltage from the LED driver circuit possible due to LED light itself have issue or the LED driver board have problem. The sound or buzzing noise from the transformer may not have a direct impact on the display. Transformer have sound could be due to the loosen ferrite core, internal winding problem or external components that caused the transformer to produce buzzing sound. If the DC output voltages from the power supply are good (even though the transformer have sound) then we do not suspect the transformer fault. Most likely either the LED driver board or the LED backlight issues.
Jestine
Joshua Oloo
November 1, 2023 at 4:26 pm
Thank you very much for the article.Am working on lcd conic 32' tv with a display shutdown,All the CCFL tubes are ok except one, and it's on a standby mode .what could be the problem sir,Thanks