LG 22" monitor - need help to confirm 2 seconds to black diagnosis

[scokljat]

Hi all!

It's a 22" LG monitor (forgot exact model, I think it's LG W2242S or similar).


Symptoms:

1. when first came to service it had 30min - 60min to black problem. Monitor powers up normally but after 30-60 minutes backlite goes black, picture is visible with a flashlight

2. I put it aside and now after few months in storage it has 2 seconds to black problem, sometimes backlite stays off after power on


Diagnosis:

1. caps looked OK and check OK with ESR meter. I replaced all caps as standard procedure

2. following "2 seconds to black troubleshooting" from this forum I came to following conclusion:

- tested LCD all four lamps on other monitor - works OK
- tested diodes and FET's - looks OK
- transformer primary (EEL-22T) - looks OK
- transformer secondary S1 - 862 ohm
- transformer secondary S2 - 886 ohm


Conclusion:

Transformer is on the edge of 3% tolerance. Transformer is BAD.


What do you think? Transformer ELL-22T with one primary and two secondaries is quite hard to find (none "T" model on ebay) and is 13$ on Aliexpress. Before I purchase, any suggestion is more than welcome.

http://www.aliexpress.com/item/EEL-2...068340157.html

Thanks!

Best regards,

Suad

[scokljat]

Re: LG 22" monitor - need help to confirm 2 seconds to black diagnosis

Help, anyone?

Thanks,

Suad

[stj]

Re: LG 22" monitor - need help to confirm 2 seconds to black diagnosis

i'd be more inclined to think one of the fets is breaking down under load.

[Th3_uN1Qu3]

Re: LG 22" monitor - need help to confirm 2 seconds to black diagnosis

i'd be more inclined to think one of the fets is breaking down under load.

Or something wrong with the controller. When transformers go bad they will either be significantly out in the lower direction (shorted turns) or completely open. What controller chip does the inverter have?

3% rule applies when you have more than one transformer, so you have a reference to work against. The values your transformer reads are close enough for it to be good.

[bammbammfran]

Re: LG 22" monitor - need help to confirm 2 seconds to black diagnosis

check your two Nikos p2503npg to see if either one may be shorted between the Drain and source or Gate. U302 like it may have run a bit hot, but that may be just the picture

also check to see if your 15 volts is dropping when it turns on

did you also try the same set of bulbs using just one set on one side of the transformer at a time to see if they flash about the same on each side of the transformer.

and did you try the screen from the unit that you tested the ccfls on to see if that screen also did not stay on (If the screen is a different size or model- do not connect the video ribbon or cable to the back of the screen- just use the bulbs)

[scokljat]

Re: LG 22" monitor - need help to confirm 2 seconds to black diagnosis

check your two Nikos p2503npg to see if either one may be shorted between the Drain and source or Gate. U302 like it may have run a bit hot, but that may be just the picture

also check to see if your 15 volts is dropping when it turns on

did you also try the same set of bulbs using just one set on one side of the transformer at a time to see if they flash about the same on each side of the transformer.

and did you try the screen from the unit that you tested the ccfls on to see if that screen also did not stay on (If the screen is a different size or model- do not connect the video ribbon or cable to the back of the screen- just use the bulbs)

Thank you for your reply. I've already tested MOSFET's with digital ohm meter set to 200ohm. When measured with transformer removed, all combinations are open. No reading at all. No shorts. I found P2503NPG MOSFET's in local shop but it's a 10$ for a piece!! Too expensive to replace just in case...

I didn't tested known good screen/CCFL's to this board. I just confirmed these CCFL's are OK connected to other monitor. I've also tried to disconnect and connect one CCFL at a time, no difference.

The thing that bothering me is the fact that monitor worked OK for 30 minutes (or more) before going to black, and now after few months in storage it has 2 seconds to black problem.

S

[bammbammfran]

Re: LG 22" monitor - need help to confirm 2 seconds to black diagnosis

you might just be getting low voltages on the power supply
Try changing the small purplish capacitor between the yellow transformer and the small heatsink . it might be a 33 or 47 x50v

on the Nikos
check to see if you are getting voltage to the gate pin on each when you power it on. Not sure what it is on these but it maybe around 5 volts

a picture of the bottom of the power board might help

[budm]

Re: LG 22" monitor - need help to confirm 2 seconds to black diagnosis

"caps looked OK and check OK with ESR meter. I replaced all caps as standard procedure" Looking at the pictures, it does not look like he replaced that start up cap.
I still like to see using test lamps on this board.