Lg 42" lc55 lcd

[junger]

Hi all, looking forward to my input into this forum. I am, I have at the moment having difficulty with the power board of a LG 42" LC55 LCD.
The sympton is the LCD switches on backlight does not light,the LCD then goes back into standby
I have replaced the PSU board and that fixed it, looking at the faulty PSU, I noticed that the large cap is bubbled at the top, any ideas please?

[billansor]

Re: Lg 42" lc55 lcd

Hi

Welcome to the forum!! This is a very informative group of people as well as very helpful! I have learned a great deal and one of the bigger things is trying to take pictures that provide a great deal of information for many of these folks. Attaching pictures is located under managing attachments.

To answer your question, the cap with the bulge was most likely leaky / drying out hence the bulge.

Replacing that cap may have fixed the set, but there could have been other issues as well as other bad filters.

Hope this helped a bit... While the information is not all inclusive, it does give you an underlying answer to your question.

Bill

[junger]

Re: Lg 42" lc55 lcd

Thanks for that, If you look at the photos, the PSU problem that I am aware of is going into standby and is sorted by changing the 10volt leaky electrolytic caps (see photos, before and after cap change). The fault that has stumped me is the large cap which is leaking but having changed that cap and the inverter the lamps still do not illuminate. It is the power board because I canged the power board from another LCD and the unit then worked. Any ideas please?

[PlainBill]

Re: Lg 42" lc55 lcd

There appears to be a high voltage supply on the lower end of the board. A good quality picture of the bottom side of the board would be a big help.

PlainBill

[1beertap]

Re: Lg 42" lc55 lcd

Two possible things to check are a shorted inverter transformer and/or a shorted power mosfet. I've circled these in the modified photo attached.

[1beertap]

Re: Lg 42" lc55 lcd

Agree with PlainBill, clear photos of the bottom of board would help.

[rmoody]

Re: Lg 42" lc55 lcd

not too sure of your photos and previous comments. Did you change some caps already? I spotted 4 bad in the first pic. I circled them below

[junger]

Re: Lg 37" 2500 lcd

Hi
Sorry, I have already changed the 10volt caps, that was to demonstrate that the 10 volt caps is not my problem (as I have done a few with that problem see cap1 jpeg which shows a replacement cap). My problem is with a LG 2500, when on analogue there are fine verticle lines down the screen when I switch to DTV, then the lines are there but no channel is shown and the set locks up. to restart the LCD it has to be disconnected from the mains and arial removed before switch on, Very strange, not come across this before. anyone know?
I will try to post some photos later

[PlainBill]

Re: Lg 37" 2500 lcd

Hi
Sorry, I have already changed the 10volt caps, that was to demonstrate that the 10 volt caps is not my problem (as I have done a few with that problem see cap1 jpeg which shows a replacement cap). My problem is with a LG 2500, when on analogue there are fine verticle lines down the screen when I switch to DTV, then the lines are there but no channel is shown and the set locks up. to restart the LCD it has to be disconnected from the mains and arial removed before switch on, Very strange, not come across this before. anyone know?
I will try to post some photos later

Well, which is it? You opened the thread with a 42" LG TV, now you are having a problem with a 37" with a different problem?

PlainBill

[junger]

Re: Lg 42" lc55 lcd

Sorry, It is a bit mixed up, I have 2 seperate faults on two seperate lcd's. I will post the correct model and the fault associated with that model.
Regards
junger

[junger]

Re: Lg 42" lc55 lcd

Ok, 37" LG has no backlight. The symptom on test is fuse o/c.
The large cap is puffed up, therefore it has probably passed a/c.
One transistor is damaged and one power diode is damaged (shown in the photos).
Replaced Cap, Mosfet and Power Diode on PSU Board (from another unit) and the LCD now has a backlight, have found a supplier for the Cap and Mosfet but cannot find a supplier for the Power Diod, any ideas anyone ?

[PlainBill]

Re: Lg 42" lc55 lcd

Ok, 37" LG has no backlight. The symptom on test is fuse o/c.
The large cap is puffed up, therefore it has probably passed a/c.
One transistor is damaged and one power diode is damaged (shown in the photos).
Replaced Cap, Mosfet and Power Diode on PSU Board (from another unit) and the LCD now has a backlight, have found a supplier for the Cap and Mosfet but cannot find a supplier for the Power Diod, any ideas anyone ?

Mouser has them in stock at $.75 each.

PlainBill

[junger]

Re: Lg 42" lc55 lcd

Sorry, have been quite ill for some time, but two stents later, better now, so am back
regards
junger