LG 42lc55 5v monitor?

[zukkermon]

Hello All

This is my first post here. My background is Motortrade (I am a MasterTech for VWG) but have an interest in electronics.

I have an LG 42lc55 with some odd goings on and am hoping someone could point me in the right direction.
The set came to me from a mate, he owned it from new, circa 3 years.
It started to shut itself down after being on for 20 mins, would just go back to standby. It could then be switched on again, but would then go back to standby after only a couple of minutes.

A repair was attempted, by a mate of his Dads. It ran fine for a total of about fourteen hours, then did the same as before.

I got the set at this point. I saw no reason to try it myself, as clearly its faulty, so proceeded to pull the back off and have a look. I found that 6 electrolytics had been changed on the power board and also found that the small board at the top, LVDS if I am right, has a small cable which had been left disconnected from the power board. I had a good look at the power board, found no reason to suspect anything silicon, both fuses intact, so went over some iffy looking solder joints and stuck it back together. It worked fine for 3 months.

It then started to go into standby immediately following switch on with the remote. What happened is that the power light went green, flashed as per normal a few times, then intermittantly you get a brief flash of the ccfls, then no picture but perfect sound for about 4 secs, then a return to standby. I re-replaced the 6 caps changed with higher voltage ones and also changed 3 others in the corner of the power board, moving them all a couple of mm off the board. 1 of them looked to be the wrong value according to a hi res pic I found online, with the same board ref and rev so I put in a 1000mf instead of the 1500mf fitted. It then worked for a couple of weeks.

Its now doing the same thing, but if I switch it on with the remote repeatedly when it fails, it will eventually startup and will then be fine for hours.

I have looked through the service menu and found under "power off"that most entries are "remcon" but there are some entries listed as "5v monitor".

Any help gratefully received!

John

[tv tony]

This is a sensible post for someone not even in the trade so congratulations, I think with a few prods in the right direction you can suss it. This chassis has been known to have its share of issues, firstly check if the ceratech mods have been done, on the signal pcb below the plug from the psu there may or not be a small row of four legged chokes, if so remove and bridge them, then come back to us,
Tony Walker. If you want i will post the official bulletin from LG

[zukkermon]

Hi Tony
Thank you for your words of encouragement! First of all, I take it the signal board is the main board in the "centre" of the set? I am unsure as to whether the ceratech filter mods have been done, the set is on my living room wall at the moment; this demonstrates how "intermittant" the fault is! I will get it down and have a look at the weekend.

I noticed another symptom, but only seen it happen once. When the set was first switched on by the remote, there was some flickering of the backlights, almost seemed to brighten for a brief moment accompanied by what sounded like an "arcing" noise from the back of the set for the duration of the flicker. Then the backlight intensity settled and all was fine.

Regarding the ceratech filters again, if you could post the bulletin, that would be a big help as i'm not too sure how to bridge them if they are four legged.

Again, many thanks!

John

[tv tony]

Here is the ceratech remedy.