inverter problem in LG 1934S LCD flatron

[stevenps]

Re: inverter problem in LG 1934S LCD flatron

U501 and U502 are Niko-Sem P6006HV(dual N-channel FET). I'll check them tonight. I didn't see any surface-mount fuses, though I'd expect the inverter would not work at all if a fuse was blown. The only fuse I see (aside from the line fuse, F801) is FB501 which is provides 12v to the inverter, and it's fine. I believe the 12v output from the power supply is actually a little over 13v, which is hopefully within tolerance.

[jetadm123]

Re: inverter problem in LG 1934S LCD flatron

I realize this thread is over a year old, but I have this same monitor and what sounds like a similar problem and I was hoping that I could get some help fixing it. The monitor is a LG Flatron W1934S and its backlight won't stay on. I replaced the caps with new ones (Panasonic FC and Nichicon HZ) but that didn't help. I have another monitor that still has original caps (Su'scon and Lelon) that behaves the same way.

After reading through some other posts, I tried measuring the voltage on the return lines from the CCFLs and I had readings all over the place. Two consistently read around 0.04v, but the other two are 0.2v and 0.7v (swapping tubes doesn't change this - the higher voltages stay with the connector). The inverter IC is a OZ9938GN (). The chip is acting like the OVP/OCP circuit is shutting things down as the voltage on pin 3 (TIMER) increases to 2.75v over about one second then the backlight turns off. What more can I do to troubleshoot and hopefully fix this monitor?

Assuming that you have verified the power supply is supplying the proper 5V and 12V outputs, you might try and check to see if there are any surface mount fuses (on foil side of board) that might be blown. If there are no fuses (or if they check good), then with power off and monitor unplugged, check U501 and U502 for shorts. These are probably dual mosfets (can't read the part number) driven by the OZ9938. If one is bad, then replace them both.

There is also the possibility that that one or more of the CCFL tubes is starting to fail.

[stevenps]

Re: inverter problem in LG 1934S LCD flatron

I realize this thread is over a year old, but I have this same monitor and what sounds like a similar problem and I was hoping that I could get some help fixing it. The monitor is a LG Flatron W1934S and its backlight won't stay on. I replaced the caps with new ones (Panasonic FC and Nichicon HZ) but that didn't help. I have another monitor that still has original caps (Su'scon and Lelon) that behaves the same way.

After reading through some other posts, I tried measuring the voltage on the return lines from the CCFLs and I had readings all over the place. Two consistently read around 0.04v, but the other two are 0.2v and 0.7v (swapping tubes doesn't change this - the higher voltages stay with the connector). The inverter IC is a OZ9938GN (). The chip is acting like the OVP/OCP circuit is shutting things down as the voltage on pin 3 (TIMER) increases to 2.75v over about one second then the backlight turns off. What more can I do to troubleshoot and hopefully fix this monitor?

[flexx]

Re: inverter problem in LG 1934S LCD flatron

oki ill take a pictures from inside and uploade it in to this forum as soon

[EGuevarae]

Re: inverter problem in LG 1934S LCD flatron

Pictures would be VERY helpful. Also, we need to know what capacitors you used as replacements, and what capacitors you took out of the monitor. Capacitor brand, series and voltage plus uF values are needed. These monitors need low ESR capacitors.

Also, there could be bad solder joints (check transformer solder joints) or dead/shorted transistors in the unit.

I agree. We need original and replacement cap info (maybe you used incorrect caps as a replacement and the problem lies there. We could not tell without the info), pictures of the boards (yes, the unit is LG on the outside, but you'll be surprised how many "brands" are brands only on the outside...and how many internal variations of the same unit exist), and that if any question arise, you can provide part info (specially on transistors/ FETs, ICs).

And welcome to the forums.

[Leopard]

Re: inverter problem in LG 1934S LCD flatron

i opened it and really changed all electrolyte caps with new , but it seems without any result

Pictures would be VERY helpful. Also, we need to know what capacitors you used as replacements, and what capacitors you took out of the monitor. Capacitor brand, series and voltage plus uF values are needed. These monitors need low ESR capacitors.

Also, there could be bad solder joints (check transformer solder joints) or dead/shorted transistors in the unit.

[Bobdee]

Re: inverter problem in LG 1934S LCD flatron

hi , i got 19 inch LCD monitor from LG model 1934S , and after using it it seems that the monitor can operate for just 5 seconds and shut down and the blue light seems the monitors is runing

i looked deeply in the monitor , ican see my desktop in very dark way without backlight

i opened it and really changed all electrolyte caps with new , but it seems without any result

this is my monitor



and please give me away to fix it and fix the backlight inverter

I guess you are right on it being inverter, but there's no info on this Monitor in forum so pics will help thoses who help you, (inverter and ps board both sides if poss)

[flexx]

hi , i got 19 inch LCD monitor from LG model 1934S , and after using it it seems that the monitor can operate for just 5 seconds and shut down and the blue light seems the monitors is runing

i looked deeply in the monitor , ican see my desktop in very dark way without backlight

i opened it and really changed all electrolyte caps with new , but it seems without any result

this is my monitor



and please give me away to fix it and fix the backlight inverter