LG Flatron W1934S problem with backlight

[DeniS182]

Hi all,
I have problem with this monitor - when I turn monitor on, it works only few minutes (approximately 5-30 min) and then backlight turn off, LED lights green, picture stay on. I measured all electrolytic capacitors on power board and all are ok, but I only replace small 47uF capacitors with a little increased ESR.
5V to logic board is ok, to inverter go 13.9V, on logic board are of course good voltages - 1.8 and 3.3V. I think the some ccfl tube is defective or only some wire had bad contact, but why it runs few minutes? Previously when I had problem with tubes it stays on only 1-2 seconds.. I add some photos when I arrive home. Could you advise me? Thanks for answer!
Denis.

[selldoor]

Re: LG Flatron W1934S problem with backlight

If it all works except the back lights it could be heat related.
Bad solder joint or faulty wiring to back lightwe will know better when we have good clear pictures- please post using manage attachments, not offsite.

Test the voltage at blon pin when the lamps are on then when off.

[DeniS182]

Re: LG Flatron W1934S problem with backlight

bl-on - 3.3V all the time when monitor is on.
Now I test it with unscrewed pcbs, without ground connected to case and it works approximately 1 hour. I test it for longer time tomorrow.

[selldoor]

Re: LG Flatron W1934S problem with backlight

I think the first thing to try would be to resolder all the connectors on both inverter transformers- better to remove the old solder and apply fresh. Do the same for the blue ceramic caps at the ends of the transformers.
Have a close look with a magnifier at Pin8 on T501 looks cracked all round in the picture.

[DeniS182]

Re: LG Flatron W1934S problem with backlight

I resolder it but it's not the problem. Today monitor runs 5 hours without turning off backlight. But when I screwed pcbs to case problem come back.

[selldoor]

Re: LG Flatron W1934S problem with backlight

OK couple of things to try:
1 Slacken off the screws - may be stressing the board in one direction.
and see if it makes a difference.
2. While it is on gently warm the boards with a hairdrier to see if it goes off quicker. If it does then try again from cold but heating smaller areas to locate the problem area.

Also re solder the Blue high voltage caps and the lamp connectors - sorry should have tagged that on to the transformers.

[DeniS182]

Re: LG Flatron W1934S problem with backlight

I tried all what you write me, but not change. It works fine all the time, but only when GND is not connected to case..

[selldoor]

Re: LG Flatron W1934S problem with backlight

OK - Not a clue

Is it the same if you only attach one board to the frame?
If you set it up outside the frame and connect a ground point to the frame with a wire does it go off? ( trying to establish if it is the grounding that makes it go off or something else.

Try it mounted on spacers/washers in case the board is bowed and touching the frame
when hot.

[DeniS182]

Re: LG Flatron W1934S problem with backlight

I tried all and I not resolve this problem. I test it with universal inverter from ebay and it works fine, but after few minutes monitor turns off and only blue led blinking. I mean it's overheating problem. Now, when I have universal inverter out from the case on air it works fine. Can you help me with this? Thanks.

[Chungalin]

Re: LG Flatron W1934S problem with backlight

I had a monitor failing the same way (backlight turned off after an hour or more) and it was a CCFL problem (upper ones). I recommend you to connect two external CCFL instead of upper lamps and try again. Anyway, replacing the lamps will be a time consuming operarion that requires a lot of skill and patience. And, unless they’re the exact replacement, you’ll need to replace all 4 lamps due to color differences.

[softman]

Re: LG Flatron W1934S problem with backlight

I am replacing the CCFL to led, i bought a kit that needs a conection between 15-30V were is recomended to do that conection? Have anyone tried this kits?
Realy sorry for my bad english.

Thanks.

[Andrew F. Ali]

Re: LG Flatron W1934S problem with backlight

To convert CCFL to LED you need to identify as follows:
1. Power Supply for LED Driver. If the CCFL Inverter was working with 13Vdc then you need a DC-DC Step-up Module Bd. to bring the supply voltage up to power the LED Driver. OR if the CCFL Inverter was working with 24Vdc then you can use this supply voltage up to power the LED Driver.
2. BL-ON, EN or SW signal would be near the CCFL Inverter supply signal wires.
3. PWM, P-Dim, Adj Control signal would be near the CCFL Inverter supply signal wires.
4. GND-Chassis ground would be near the CCFL Inverter supply signal wires.
You would have to remove the CCFL and its supports and any other circuit Bd. in the Panel. The only thing you would re-use would be the white Reflector sheet that you would have to cut some holes to properly fit the LED lens through and re-use the Polariser and Prism sheets in the same order you removed them.