inverter problem in LG 1934S LCD flatron

[nikoslemnos]

Re: inverter problem in LG 1934S LCD flatron

The output voltages of the inverter are in the order of 1KV at 40 Khz. That is beyond the normal capabilities of a DMM, and trying to measure it can kil a DMM.

PlainBill

Thanks PlainBill.. my concern also.... I will try to replace the two power mosfets (AP9971GD IC's) and see if that fixes things...

[4z4rb]

Re: inverter problem in LG 1934S LCD flatron

After reading all 4 pages I will see about my monitor
it has the same 2 seconds problem. before it died on me it used to flicker once or twice on start and work ok it did it 3 or 4 times and zapp
only on reseting the AC it will start and show for two seconds and then .....
thanks

[selldoor]

Re: inverter problem in LG 1934S LCD flatron

Hi - welcome to the forum - having read your introduction I doubt there is much I can help you with - fortunately there are much more experienced members and hopefully you will join as a contributor.
As you will have seen there is a schematic for this at elektrotanya.com and retiredcaps guide to 2 seconds to black is good - it has been updated and now starts at #19 .
If you get stuck many will help - if you post pictures please post pictures of each board, front and back 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...1&d=1290283049

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

[vakar]

Re: inverter problem in LG 1934S LCD flatron

Thank you very much all contributers, especially PlainBill, alexanna and stevenps and others. I had an Lg w2253s monitör not working. The problem was after I turned on the monitör it stayed on about 1/2 seconds and it got completely black, after about 20 or 30 seconds it turned on and stayed for another 1/2 seconds and then it got black screen again. I could see nothing. But the stand up light was still blinking.
After I read this article about lg monitors I decided to dissassamble the monitor and change the cold-cathode fluorescent lamp ( CCFL). First I checked the power board very carefully. There was no problem with the power board and inverter. While I was dissambling lcd part it I realized that one of the wires welded to the one side of the CCFL was broken. Probably it would work again if I soldered the wire to the place where it detached . But I had learned sometimes ago that you can replace lcd flourescent lamps with a led kit with lamps. I bought it and changed with the led lights. It worked. Finally my lcd monitor turned to be a led monitor. Thanks a lot.
VK

[Lumberjack777]

Re: inverter problem in LG 1934S LCD flatron

But I had learned sometimes ago that you can replace lcd flourescent lamps with a led kit with lamps. I bought it and changed with the led lights. It worked. Finally my lcd monitor turned to be a led monitor. Thanks a lot.
VK

Nice job!

[jay1]

Re: inverter problem in LG 1934S LCD flatron

I have the same monitor. here is my problem:

when i turn on the monitor in the morning, it works for 15/20 minutes then display goes black. the power LED stays on (blue). If i push the power off and turn on again (right way) i see the display for a second, then it goes back black. If i wait few minutes then turn on, then displays says for few minutes then goes black.


I opend up and inspected the capacitors visually. they all looks great. I didn't find any other damage or loose connection (visually) either.


then i thought may be its overheating. so i open the back and placed a table fan on full speed. it worked for hours! after half an hour it flickered a little, but did not go black. after about 3 hour it finally go black (with the fan on). in another word with the fan on it works longer the the problem is there.

so what is the problem? or what can i do to isolate the problem?

thanks

[lexwalker]

Re: inverter problem in LG 1934S LCD flatron

I have the same monitor. here is my problem:

when i turn on the monitor in the morning, it works for 15/20 minutes then display goes black. the power LED stays on (blue). If i push the power off and turn on again (right way) i see the display for a second, then it goes back black. If i wait few minutes then turn on, then displays says for few minutes then goes black.


I opend up and inspected the capacitors visually. they all looks great. I didn't find any other damage or loose connection (visually) either.


then i thought may be its overheating. so i open the back and placed a table fan on full speed. it worked for hours! after half an hour it flickered a little, but did not go black. after about 3 hour it finally go black (with the fan on). in another word with the fan on it works longer the the problem is there.

so what is the problem? or what can i do to isolate the problem?

Try to look for cold/dry solder joints. There's also the possibility that some of the SMD capacitors in the inverter feedback and protection section is failing.

[jay1]

Re: inverter problem in LG 1934S LCD flatron

thanks lexwalker.

cold/dry solder joints

last time I inspect everything looked pretty steady. i'll look again. but does a "dry solder joints" explains the display off with heat up?

SMD capacitors in the inverter

well capacitors on the inverter board are really tiny. are they replaceable (by a non prof person like me)?