LG W2442PA backlight blinks out for a few seconds

[Freydnot]

I have a LG Flatron W2442PA (actually I have two but only one is acting up) that has been in use for a few years. Recently the backlight cuts out and then comes back after a few seconds. A few weeks ago when it started, it did it every day or two. Now it is doing it every minute or so (randomly). Occasionally the picture will have a bunch of lines for a split second but that isn't very often.

This unit has two boards; a power supply board and a logic board.

I'm guessing since the backlight wires connect to the power supply board, that's where the problem is.

A visual inspection shows the caps look okay, but there isn't any way to be sure.

I'm thinking the easiest thing to do is replace the electrolytic caps and see if that fixes it. (see the attached pics for component IDs) I'm thinking C203, C204, C205, C206, C212 for sure, probably C301 and maybe C103 and C105.

C101 and C108 look fine and I'm guessing I would have bigger problems if they were going bad.

Does this seem like a sound plan? If not, what would you recommend?

I've attached a service manual.

I've got a Fluke 79 meter, a soldering station and many years of experience soldering.

I'll post more pics in the next messages.

[Freydnot]

Re: LG W2442PA backlight blinks out for a few seconds

Various pics of the power supply board.

[Freydnot]

Re: LG W2442PA backlight blinks out for a few seconds

A few pics of the logic board...

[dj_ricoh]

Re: LG W2442PA backlight blinks out for a few seconds

can you do something hard? or do you wanna do something rly hard?

check the lamps on the panel !
don`t take them out just check them.

if you got some spares that will be nice ^^

I`ll say that this is the first thing that I will do.

[Freydnot]

Re: LG W2442PA backlight blinks out for a few seconds

I could do that. What would I be looking for in the CFLs? A crack or something?

It seems to me if one of the CFLs were going out, the display would only dim (since 1 of 4 lamps is out). In my case, it goes totally black.

[selldoor]

Re: LG W2442PA backlight blinks out for a few seconds

Looking cracks or blackened ends burnt wiring.

On most sets if one lamp fails protection kicks in to protect the inverters and ALL lamps switch off.

As you have another monitor you could open it up and plug in the panel from that
just as a quick test. Or build two test bulbs for 14w or less cfls

[Freydnot]

Re: LG W2442PA backlight blinks out for a few seconds

Good idea. As soon as I get time I'll take the second one apart and swap power supply boards. That should tell me where the problem is (and I won't have to dig into the LCD assembly).

[Agent24]

Re: LG W2442PA backlight blinks out for a few seconds

In one monitor that had 3 dying lamps, I saw no issue with the picture at all. Lines through the picture might mean PSU problem causing both picture and lamp issue. Perhaps.

Swapping PSU boards at this point will be a good test.

[Freydnot]

Re: LG W2442PA backlight blinks out for a few seconds

Well. I swapped the power supply board and now the problem seems to have gone away. Both monitors are working properly.

Maybe the wires inside were just lonely and needed some attention.

Now the waiting game to see if the problem comes back.

[Agent24]

Re: LG W2442PA backlight blinks out for a few seconds

If you prove it's the PSU...
Check the capacitors on the bad PSU. Su'scon aren't renowned for being high quality.

Check all the solder joints, especially in the inverter section and around the transformer\coils and driving transistors etc. This is quite likely, bad solder in LCD monitors happens often and the fact that the problem went away after moving the PSU could indicate an intermittent connection somewhere.

[Freydnot]

Re: LG W2442PA backlight blinks out for a few seconds

Well, two days of use and they are still both going strong. I notice the "problem" monitor that I swapped the "good" power supply board into seems brighter. I had to crank the brightness way down to get a good match with the other monitor.

[Agent24]

Re: LG W2442PA backlight blinks out for a few seconds

That could be an indication of the old PSU having an issue with low voltage in the inverter

[Freydnot]

Re: LG W2442PA backlight blinks out for a few seconds

Today I noticed the upper left corner of the problem monitor (the one that now has the "good" power supply in it) is looking a bit bluish. It doesn't show in a photo, but my eyes notice it. I'm guessing this means I've got a lamp that is going bad and was probably the cause of my original problem?

Since I was placing an unrelated order at mouser, I ordered some new Panasonic caps for fun. I'll probably swap them as a precautionary measure the next time I have it open.

Any advice on the lamp? How does one go about replacing a lamp? Is it wise to replace a single or should you really do all 4 while you are in there? Are lamps expensive? Where does one get lamps anyway?

[Agent24]

Re: LG W2442PA backlight blinks out for a few seconds

At a guess I would say there is something wrong with the phosphor coating on the lamp and the blue you are seeing is probably light in the near-UV spectrum coming out where it should not.

Likely the lamp is bad and the old inverter was shutting it down, the new one may not be as sensitive...

You can get new lamps on eBay and other places, quite cheaply. You need to know the dimensions of the old lamps. Replacing them is possible and not extremely hard, but you have to take care not to damage the panel or the lamps.

[stj]

Re: LG W2442PA backlight blinks out for a few seconds

or you can get an led upgrade kit.

[Agent24]

Re: LG W2442PA backlight blinks out for a few seconds

https://www.badcaps.net/forum/showthread.php?p=477574 mentions having blue on his backlighting possibly due to a bad cable.