LG Monitor cum TV RT-15LA31

[jdwis]

Hello

Got this one to repair. The symptoms are, it flickers when turned on and keeps flickering. Opened the back cover but couldnt find any bad cap. This one requires 12V DC external supply, I did not have one so used a computers power supply and connected dc jack to it to power up the Monitor/TV.

It fired up but the screen shows plain raster with continuous flicker. Thought of bad CCFL as well, I had spare CCFL from some TV so used that to check it, the good CCFL were also flickering. The inverter has OZ960 chip, and 2 CCFLs.

As I have 2 extra CCFLs it helped in checking this. I had little surprise in checking. My thought is if only one CCFL is connected and other not, then the inverter should sense missing or broken CCFL and should power up once and should go black. But it did not happen, it kept flickering 1 CCFL - the only one connected.. ??
Is it normal?
I have checked both the transformers, they are good, secondary impedence/resistance shows upto some 976 etc on both and seems ok.

couldnt get a clue to find fault further?

[selldoor]

Re: LG Monitor cum TV RT-15LA31

Think we are going to need pictures for this one.

We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back (in the same orientation) and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed

https://www.badcaps.net/forum/attach...7&d=1280167246

https://www.badcaps.net/forum/attach...6&d=1280167246

https://www.badcaps.net/forum/attach...4&d=1280167246

It will be useful if you can say what the supposed fault was and a bit about yourself - skills tools etc.

[retiredcaps]

Re: LG Monitor cum TV RT-15LA31

My thought is if only one CCFL is connected and other not, then the inverter should sense missing or broken CCFL and should power up once and should go black. But it did not happen, it kept flickering 1 CCFL - the only one connected.. ??
Is it normal?

Generally yes you are correct in the above thinking. The pwm IC should turn off the ccfls after a couple of seconds.

If the pwm IC isn't shutting off the ccfls, it could be

a) the pwc IC isn't working correctly
b) someone worked on this lcd and disabled the functionality by removing something in the sense circuitry

[jdwis]

Re: LG Monitor cum TV RT-15LA31

I was rushing out so couldnt post any pics, I will put the pics 1st thing tomorrow morning.
Anyways out of curiosity even if the cpapcitor was ot looiing bad I changed it and it gavw continuous display without flicker.

But now it does not show the PC input, even if the cable is connected and changing the monitors source to PC, it does not show the PC display.

[jdwis]

Re: LG Monitor cum TV RT-15LA31

Good Morning & Merry Christmas

Here are some pics, my camera is not so good so tried to take some better pics, if needed more for any specific section pls just say and I will take it quickly.

The flickering is sorted but the pc display is not showing.

[selldoor]

Re: LG Monitor cum TV RT-15LA31

Happy Christmas
I am away most of today is your screen just all white or all black

Check the fuse ( F1 small white) on the inverter board.

Check all cables plugged in firmly - which is the one to the panel?

Can you get to the panel end of it - is there another board?

[jdwis]

Re: LG Monitor cum TV RT-15LA31

Inverter board is fine, its working properly now as the flickering is sorted, so no problem with the inverter.
Now the problemis with the Main Board. None of the inputs are producing any signals.
A/V, PC, S-Video - none bring any signal on the display. All remains blank.

[selldoor]

Re: LG Monitor cum TV RT-15LA31

It would be really helpful if you would answer the questions as asked.

[jdwis]

Re: LG Monitor cum TV RT-15LA31

Check the fuse ( F1 small white) on the inverter board.
Check all cables plugged in firmly - which is the one to the panel?
Can you get to the panel end of it - is there another board?

my dear friend selldoor
Q: Check the fuse ( F1 small white) on the inverter board.
A: The fuse on the inverter board is fine, I have checked it, its located near the connector.

Q: Check all cables plugged in firmly - which is the one to the panel?
A: The one on the right bottom is the power connection to the onboard power plug (black + red) as I did not have similar power pin adapter so just soldered another 12V power cable to it.

Q: Can you get to the panel end of it - is there another board?
A: Right top board is Main board. Left top connected is inverter, another small to its right is buttons board and finally to the bottom left is On/off switch + remote sensor board.

All the cables are connected properly, the one you see on the top left corner doubts a bit but is by default not connected and remains empty.

The thread originated with the problem of flickering display but as I mentioned earlier it is now resolved, further checking shows that connecting any of the sources (A/V, S-video, PC) would not bring any picture.
So stuck here.

[selldoor]

Re: LG Monitor cum TV RT-15LA31

Does the screen remain Black or white?

There should be two fuses on the main board but you picture is not clear enough for me to see them - They could of course be on the back but you have not posted a picture of that yet.

Is there any sound.

Is the power supply you are using sufficient amperage

[jdwis]

Re: LG Monitor cum TV RT-15LA31

The screen shows menu etc quite clear, I did previously connected power supply with less Amp and it didnt even broght the screen, so used another higher Amp one and that is fine in lighting the screen so ext PS is ok as the Menu etc is seen quite clear without any prob.
The display does bring light but no details of source like pc etc so its not dark as if a fault in inverter, not like that (CCFL lights up and stays on).
Sorry m8 dont have a good camera and due to inhouse lighting couldnt get much clear pic, will try sometime in day if I could get more clear pic.
At present I am attaching another pic of back. I do have service manual, can I attach it here?
Though the service manual is not too clear to get quite detail from it, trying to make some sense from service manual though.

Also couldnt find any obvious fuses on the board, but if you say so I am checking it again but surely its not there, the only I cold spot was on inverter.

[jdwis]

Re: LG Monitor cum TV RT-15LA31

I checked supply voltages on most of the ICs, and it seems ok to me, the RESET pin is high on few ICs, could that be the case or anything else?