LG 42LG50 Works ... sometimes

[drpj23]

Ok, so this LG (when it doesn't work) will power on but there will no be no backlight (i haven't been able to tell if there was still a picture since it hasn't failed again to let me do that). And it will do it off and on. Other times it works great.

I have checked the other posts and most were having issues with the fuses but all checked ok even the black one.

The only difference between that one was that the ON/OFF pin was only .84v instead of the 3.3 needed (except when working).

Any ideas?

[cadiman]

Re: LG 42LG50 Works ... sometimes

I have not had any issues with this power supply. Looks like you have the good panel too.

The Mainboard has been an issue with these sets.

There should be a 24 volt feed to both inverters when powered on from the power supply.

This is the last of the good L/G tvs.

[drpj23]

Re: LG 42LG50 Works ... sometimes

Is there any way to be sure of the main board?....I honestly want to say inverters but have not a clue to be certain about it.

Oh and there is 24v there. The only different voltage was that ON/OFF one so I can see why it could be the main board.

Ok, unless i get any other advice, I may just shotgun it.

[retiredcaps]

Re: LG 42LG50 Works ... sometimes

The only difference between that one was that the ON/OFF pin was only .84v instead of the 3.3 needed (except when working).

1) The main board, which is hidden in your picture, generates the on/off signal.

2) Check the voltage regulators on the main board (see my sig file below).

3) Provide a clear focused picture of the main board.

4) You may have bad caps on the main board.

[tibimakai]

Re: LG 42LG50 Works ... sometimes

I have a 42LG70 which blows the fuses. I have replaced all the capacitors, since they were of low quality.
I still couldn't fix it yet. Same exact power supply.
It couldn't be a small startup capacitor causing this issue?

[cadiman]

Re: LG 42LG50 Works ... sometimes

a 42lg70 is worth fixing.

I have not had issues with this type (power supply). I would still replace any caps at stand-by part of supply.

I have not had to troubleshoot these inverters.

The mainboard issues I have had were not related to backlight control.

[drpj23]

Re: LG 42LG50 Works ... sometimes

Well I just went ahead and ordered the main board so we'll see I guess and then go from there but thanks for the regulator tips though.

[drpj23]

Re: LG 42LG50 Works ... sometimes

Well i just installed the main board, and now the voltages are:
BRI - .49v
ON/OFF- 3.3v
PWM-DIM- 1.4v
ERROR- 0v

I do not see any backlight nor an image (but conditions might just not let me)

Thoughts? Does 0v on error mean ...error?

[budm]

Re: LG 42LG50 Works ... sometimes

Do you have the LCD panel make and model?
Is this "ERROR" pin at the inverter board or at the main board?

[drpj23]

Re: LG 42LG50 Works ... sometimes

I can get that tuesday for you (the make and model) and at the inverter board.

[budm]

Re: LG 42LG50 Works ... sometimes

The LCD panel spec sheet will give the information for the Inverter and the T-CON board pin outs and functions. It will tell you if the 0V on error pin is = good or not.

[drpj23]

Re: LG 42LG50 Works ... sometimes

Although I have to give it back (i was working on it for someone) if it is relevant, V420H1-L12 is the panel.