CCFL transformer smoking and burning

[JoeyJoe]

I have a 1080p 22" LG TV/Monitor that has been fading to black after a few seconds, with a display still on the screen, just the back light that goes out.

After some playing around, the back lights managed to stay on for roughly 2 minutes before the transformer started to smoke and burn, the light stayed on during this.

Would this be a bad transformer, or could it be a bigger problem and the burning of the transformer being a symptom?

Thanks!

[tom66]

Re: CCFL transformer smoking and burning

This could indicate a shorted output on the transformer, for example, a CCFL wire that is loose but shorting to the case. The transformer could also be defective or the power MOSFETs that drive it might be too.

[JoeyJoe]

Re: CCFL transformer smoking and burning

Ive checked all the CCFL wires and they seem to be fine.

I couldn't find any info about "MOSFETs". Could you explain to me what these are and how I could test it?

Thanks!

[selldoor]

Re: CCFL transformer smoking and burning

Google is a great tool?

We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

https://www.badcaps.net/forum/showthread.php?t=25836


I am not sure why you have started a new thread? you are still fixing the same set.

[JoeyJoe]

Re: CCFL transformer smoking and burning

Thanks for your reply. I checked google and it didn't explain anything to me. All I managed to find was a single image on google of something else on the board.

I have also gone though the guides on this forum but they are not in depth enough. They explain how to basically check a 8 pin inverter / transformer but not the one I have which is 6 pin. I tried to follow the guide but didn't get anywhere with it at all since it does not explain how to identify the pins.

I also made another thread on a different forum since people stopped replying to my other thread. Obviously this would be the only next logical thing to do to ask for help?

[budm]

Re: CCFL transformer smoking and burning

Any good, clear, focused pictures of the board and the burnt out transformer? Model number of the board, the TV/MONITOR?

[selldoor]

Re: CCFL transformer smoking and burning

Thanks for your reply. I checked google and it didn't explain anything to me. All I managed to find was a single image on google of something else on the board.

Well you must have a different Google than I have?
Your question was what is a Mosfet - type" what is a mosfet" into a search and you will almost certainly get this.
http://en.wikipedia.org/wiki/MOSFET.

Next - How do I test it.
In the link Tom66 provided in your other thread and I provided there is a guide
2 seconds to black.

Mosfets

If you have a manual range multimeter, set it to 200 ohms (two hundred). This is for 3 pin ICs only. You can test a mosfet (Q, IC designation) "in circuit" by (power off and unplugged)

a) black on pin 1- red on pin 2 - record ohms
b) black on pin 1- red on pin 3 - record ohms
c) black on pin 2- red on pin 3 - record ohms

If any reading is less than 30 ohms you might have shorted mosfet. Remove from circuit and repeat the tests to verify.

Some mosfets are more than 3 pins. To test those, identify the part number and search for its datasheet. Once you find the datasheet, the pins will be designated source (S), gate (G), and drain (D). It will probably be documented as S1, S2, G1, G2, D1, D2.

Simply test

a) black on pin S1- red on pin G1 - record ohms
b) black on pin S1- red on pin D1 - record ohms
c) black on pin G1- red on pin D1 - record ohms

Repeat for the "2" pins. That is S2-G2, S2-D2, G2-D2.

Note: a shorted mosfet would likely cause a very brief flash of the backlight or no backlight.

Here is a case study.

https://www.badcaps.net/forum/showthread.php?t=17659

I have also gone though the guides on this forum but they are not in depth enough. They explain how to basically check a 8 pin inverter / transformer but not the one I have which is 6 pin. I tried to follow the guide but didn't get anywhere with it at all since it does not explain how to identify the pins.

The tests are more in depth than you need - The instruction for inverter transformer will cover any number of pins in any configuration.
In the same 2 seconds to black guide

4) Bad inverter transformer

The transformer (T designation) converts the low voltage into high voltage to drive the CCFLs. These can be bad. A simple test is to measure the resistance of the secondary windings. If you look at the transformer, these will be the thinner guage windings/wires. Sometimes you can tell which are the secondary inverter transformer pins. If you cannot, then you have to use "brute force" and measure all possible combinations as explained below.

If you have a manual range multimeter, set it to 2k ohms (two thousand). You can test for open windings "in circuit" on the transformer (with power off and unplugged).

Power off and unplug monitor. WAIT 5 MINUTES BEFORE STARTING the ohms measurements. Waiting allows the capacitors and other components to discharge.

a) Number the pins on the transformers anyway you like
b) black probe on pin 1, red on pin 2 - record ohm
c) black probe on pin 1, red on pin 3 - record ohm
d) black probe on pin 1, red on pin 4 - record ohm
e) etc
f) black probe on pin 1, red on pin last - record ohm
g) black probe on pin 2, red on pin 3 - record ohm
h) black probe on pin 2, red on pin 4 - record ohm
i) etc
j) black probe on pin 2, red on pin last - record ohm
k) black probe on pin 3, red on pin 4 - record ohm
l) etc
m) finally, black probe on pin last-1, red on pin last - record ohm

A 3% variation or more in the secondaries suggests a bad transformer. For example, if one reading is 950 ohms and the other is 750 ohms, then one of the transformers is bad.

This test is not exhaustive as it does not detect all faults.

Here is an example of what to measure.

http://lcdparts.net/TransformerDetai...ProductID=2724

Here is a case study.

https://www.badcaps.net/forum/showthread.php?t=12121

I also made another thread on a different forum since people stopped replying to my other thread. Obviously this would be the only next logical thing to do to ask for help?

We are all volunteers on this site - we all have lives outside trying to help on badcaps. There are only perhaps a dozen regulars and hundreds of posts a day. As we can only attempt to help some, we can choose which ones we want to help. Most help tends to goes to those who help themselves and if you had studied previous threads you may have realised that.

Unfortunately you unwittingly probably put off a number of helpers by
1 Posting a picture of a board off the internet instead of your own.
2 Posting a picture in Line instead of using " Manage attachments"

and now
3 Double posting the same problem - when you do that some information is lost and we dont have time to skip back and forth between threads.

So I suggest you read the 2 sec to black guide again - start at post 19.

Then post pictures of your boards - this is my usual instruction

We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back (in the same orientation) and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed

https://www.badcaps.net/forum/attach...7&d=1280167246

https://www.badcaps.net/forum/attach...6&d=1280167246

https://www.badcaps.net/forum/attach...4&d=1280167246

It will be useful if you can say what the supposed fault was and a bit about yourself - skills tools etc.

Finally is there a part number on the transformer.

[JoeyJoe]

Re: CCFL transformer smoking and burning

Sorry and thanks.

I removed the transformer and tested. It was fine.

As I were soldering it back, I noticed a bad solder. After reconnecting, seems to be working ok. Will run it up and leave it outside for an hour to see if the thing burns up

[selldoor]

Re: CCFL transformer smoking and burning

Hey - that is good news - let us know how it goes. just for the record
As advised in another thread the board is a PLLM-M702A
which is correct for this model.LG M227WJ
The transformer (from other ebay pics) seems to be an EEL22T. which is also known as a TM1126A

http://www.iccfl.com/popup_image.php...j1nji3mfst0de5

[JoeyJoe]

Re: CCFL transformer smoking and burning

Well it worked for about 10 minutes before cutting out again, now its back to the 2 seconds to black.

Aha that is the correct transformer. Thing is I removed the transformer and tested the terminals, I'm getting 1010ohm on both secondary and the primary was fine too. Stumped again!

[selldoor]

Re: CCFL transformer smoking and burning

Bummer! As you have two sets open can you plug the panel lamp leads from the other one into this one (even one or two, if they wont all reach)

Trying to eliminate bad bulbs/wiring.