LG w2241s 2sec and then black

[rippergr]

Hello,
this is my first post (and repair try) for an lcd screen except bad caps.
I have an LG W2241S that when I turn it on it stays on for 2-4 seconds and then goes to black.
I checked for bad caps , all seems fine, I put good lamps it does exactly the same.
Can someone tell me where to start looking and how and what to measure.
I am attaching a few pictures from the lcd.
Thanks in advance.

[rippergr]

Re: LG w2241s 2sec and then black

P.S. I try with one new lamp at a time. Same problem.
The transformer in the secondary winding has 1011 ohm one one side and 1024 ohm on the other side.
Primary winding shows 000 ohm ( not open )

[budm]

Re: LG w2241s 2sec and then black

You should use two test lamps at a time since you can have two bad lamps in one lamp assembly.
I.E.
http://s807.photobucket.com/user/bud...ml?sort=3&o=11
http://s807.photobucket.com/user/bud...ml?sort=3&o=10
http://s807.photobucket.com/user/bud...ml?sort=3&o=32

[rippergr]

Re: LG w2241s 2sec and then black

I first try with two new lamps.
Then I used one good lamp only and no second lamp.

[bammbammfran]

Re: LG w2241s 2sec and then black

usually not all 4 bulbs will go bad at one time , but ??
You do need 4 working bulbs for it to stay on
to try to figure out if it is bad bottom or bad top bulbs:
you need to use two new lamps on the bottom two plugs and put two old top lamps into the top two plugs and try it.
and if that does not stay on, install the two new ones into the top two plugs and the 2 used bottom ones into the bottom two plugs
if your new bulbs do not at least flash on on the top 2 or the bottom 2 , then the transformer might be bad.

[budm]

Re: LG w2241s 2sec and then black

I first try with two new lamps.
Then I used one good lamp only and no second lamp.

How did you go about testing using the two lamps and one lamp only?

[rippergr]

Re: LG w2241s 2sec and then black

When I say one lamp I mean one pair of lamps
I have attached a picture.
So I test it with 4 new lamps (2 pairs) and it does the same problem.

[selldoor]

Re: LG w2241s 2sec and then black

Looking at the picture of the back of the board the soldering on at least one
pin of the transformer looks suspect.
As it seemed to resistance test ok I would reflow all the joints on the inverter transformer,
and while you are in there reflow all the blue high voltage caps as well.

[rippergr]

Re: LG w2241s 2sec and then black

Looking at the picture of the back of the board the soldering on at least one
pin of the transformer looks suspect.
As it seemed to resistance test ok I would reflow all the joints on the inverter transformer,
and while you are in there reflow all the blue high voltage caps as well.

This is just soldering paste. I reflowed all the joints in transformer and in all blue caps but still the same problem

[budm]

Re: LG w2241s 2sec and then black

OK, there are two SMD Duld MOSFETS (4 legs on the bottom and big tab on top) that drive the inverter transformer, please get the numbers and look up the spec sheet.

[rippergr]

Re: LG w2241s 2sec and then black

OK, there are two SMD Duld MOSFETS (4 legs on the bottom and big tab on top) that drive the inverter transformer, please get the numbers and look up the spec sheet.

You mean those 2 MOSFETS?
Sorry but I am newbie

p.s: those mosfets are APM4048D WJC3V
I found that the specs are here http://www.anpec.com.tw/ashx_prod_fi...APM4048DU4.pdf
Can you tell me how to check?
Thanks

[budm]

Re: LG w2241s 2sec and then black

Yes.

[rippergr]

Re: LG w2241s 2sec and then black

Can you tell me how to test the MOSFETS?
Do I have to unsolder them or I can measure them on circuit?

[selldoor]

Re: LG w2241s 2sec and then black

If you have 2 seconds to black you should read this
https://www.badcaps.net/forum/showthread.php?t=10419

start at post 19. There is a section on testing mosfets.

First you just test them for shorts so you can do that on the board
with NO power to the board.

If you get stuck ask again - if you understand it, post your results.

[cdicky]

Re: LG w2241s 2sec and then black

Sorting my tv out a few weeks back, i found a lingk on youtube showing the lamp good circuit for each lamp. Some sort of nandgate. If the current (voltage) goes too high it shuts off supply to inverters. Spent weeks sorting mine out, from psu caps to swapping inverters. But even after all that still tripped to black after few seconds.

Eventually after testing everything and loads of 'repairs' 'it HAD to work and was back together and on the wall. Could have cried when it just went again.
So thought F** IT. And just kept turning it back off/on with standby button as soon as screen went off.
Funnily enough after about 60 times, (was better than throwing remote at it) I decided this thing was gonna either fry or work. And eventually heard a large crackle and sizzel.
So did it a few more times and guess what, damd thing has worked fine ever since.

And my verdict? well initial faults were poor psu no doubt. But all that handling and moving (big TV) just made things lose. Face down it worked Ok after repairs, but on the wall it would die and go black again.
Until it had a good supply to work with I reckon it arced over one of the lamp contacts, and when it did so welded a poor connection.

So rather than replace all the lamps, give that a look.
And good luck

[rippergr]

Re: LG w2241s 2sec and then black

I think it's the MOSFET.
I test it based on selldoor post.
With my multimeter on 200 ohms I checked
Black S1 - Red G1 = infinitive
Black S1 - Red D1 = sometimes increase value to infinitive , sometimes infinitive
Black G1 - Red D1 = infinitive

Black S2 - Red G2 = infinitive
Black S2 - Red D2 = infinitive
Black G2 - Red D2 = infinitive

The second MOSFET doesnt clearly show values . sometimes show some ohms and go to infinitive

[selldoor]

Re: LG w2241s 2sec and then black

They actually look ok to me as long as there are no readings less than 30 ohms
it suggests they are ok. I will try and think of some other tests hopefully Budm will look in a again later

[vinceroger69]

Re: LG w2241s 2sec and then black

whats the part number on the inverter transformer?

[rippergr]

Re: LG w2241s 2sec and then black

its not very clear. The numbers I see are EBJ5753( some numbers under a sticker)
right under that eel-220
right under TC 0844

[vinceroger69]

Re: LG w2241s 2sec and then black

are these numbers off the picture post 1 the black oblong transformer top off picture?