LG 50PX4R-ZB stuck in standby mode

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

Most multimeter capacitance ranges are not useful for testing capacitors to see if they are working, only to characterise them if you do not know their value for example. The 330uF should all test at 330uF+/-20% but there are many in parallel which will change the reading plus other components too.

Your particular fault would not be caused by a bad capacitor with low capacitance as it would not cause a short.

One way to try tracking down the short is passing a current through the Vs and GND and seeing what heated up, which would indicate where the short is. You could use for example a 12V battery and a 12 ohm, 15W resistor. The trouble is the current may have to be very high to make any noticeable heating occur.

OK thanks Tom for your help .... I wish i never got an LG TV now ... should of got a Samsung instead !!

I suppose my only hope then is to either wait and buy a YSUS board or put it back together and sell as spairs/repairs

Thanks again

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

Ugh, Samsung fail just as often if not more than LG. Panasonic or Pioneer maybe, but very expensive. And Pioneer stopped making TVs now. And newer Panasonic TVs are poorly made. So.....

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

Hi again

I tested out the YSUS board again with my muti meter set onto continuity with the beeping
and vs is not toning out with ground ?? does this mean it might not be the YSUS board ??
I am just so uncertain and with already buying a main av board which I cannot sell I don't really want to buy a YSUS board only if it is definitely this that needs replacing ??

Thanks for any help

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

Hi Tom ..... I am hoping that i have found the fault ????

I checked readings on all 25V 330uF 105 C capacitors and have attached a couple of pictures

There seems to be a reading difference on one of the 25V 330uF 105 C

C88= 370 is this too low ?
C90= 1390
C102= 1390
C1=1327
C2=1375

I Had my meter in the 2000uF range

Is Capacitor C88 my problem ?? I really hoooope sooo ??

thanks steve

I know I am clutching at straws here but I suppose I have every reason to ???

Double checking back on the thread ............. Can this capacitor be the cause of my problem ???
Now that I used a different multi meter with continuity beep there does not seem to be a short between Vs and GND just 130 ohms NO BEEPING OR CONTINUITY ??
PLEASE NEED HELP !!! before spending over £100 on a YSUS board I might be able to fix ????

Thanks to anyone who can help me !!!!

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

Hi Tom

Yes the RL ON and Vs ON go from the power board to the AV board with the video inputs on.

On this board there is a red led light on ? Does this red light on the av board indicate a fault ?

I have attached some pictures of the board. Do you know anywhere that i can get this board from ? I have tried ebay but there is only one for a 42" TV

Thanks again for all your help Tom !!

Another thought looking back at the thread and when Tom thought I needed a new main board. This was because the Vs ON was not getting any voltage when powered up ??
Well the the RL ON and Vs ON go from power board to the main board ?
Now could it be the power board ?? as it is the Vs which is not getting voltage maybe from the power board ???

ANY HELP APPRECIATED AND THANKS AGAIN IN ADVANCE AND YES I AM A NEWB !!

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

HELP NEEDED PLEASE !!!

I have just found a diagram which shows me that AC DET goes from the power supply to the main board I have tested and have 4.3 volts going from it BUT not 5v ??

The diagram then tells me that the main board processor then switches the VS ON but if no AC DET the tv will turn off ?? well this is whats happening but the main board is getting AC DET 4.3v ???

The diagram also says that I can force the VS ON by putting a 100 ohm resistor across STBY 5V and VS ON

Will this get my TV working ???

Thanks again for help I am literally tearing my hair out !!!

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

4.3V is fine for an AC detect circuit. Below 2V is generally considered bad.

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

4.3V is fine for an AC detect circuit. Below 2V is generally considered bad.

Hi Tom

As mentioned I am a newb but I have looked at the manual for the power start up sequence which ive attached.
1. AC in PSU yes
2.STBY5V out to main board Yes
3.AC DET to main board Yes
4.power to front IR board Yes
5. RL ON (relay on 5v to PSU Yes
6. 5V MNT from PSU NO

Could this be the Problem ????

If I linked the 5v STBY to 5v MON and Vs ON could this in effect make the TV work ??

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

4.3V is fine for an AC detect circuit. Below 2V is generally considered bad.

sorry forgot to attach the picture !!

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

I really doubt a 50PQ30 manual will be applicable to your 50PX4R? Am I missing something here?

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

I really doubt a 50PQ30 manual will be applicable to your 50PX4R? Am I missing something here?

I just presumed that these LG TVs would have the same principles behind them ? I know they are different models but surely they must work in the same way ??? If so would it not suggest that the power supply is not triggering the 5vMNT back to the main board resulting in the main board not triggering the Vs ON or 5v MONI

I am probably barking up the wrong tree again !!!!! I cant find an exact manual for LG50PX4R

What would you suggest ?

Thanks

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

They have made so many changes so they wouldn't be compatible, 50PQ30 I believe is a 2009 or 2010 TV and yours is 2006/2007. I don't know what to suggest unfortunately.

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

They have made so many changes so they wouldn't be compatible, 50PQ30 I believe is a 2009 or 2010 TV and yours is 2006/2007. I don't know what to suggest unfortunately.

mmmmmmmm ??

What about if I link the 5v to 5V MONI this might then trigger the VS ON ???

I will keep looking for the manual but its not looking good

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

I don't think so; why do you think that will work?

It looks to me like your main board has a problem meaning it won't power up for some reason or another.

Even if you do jumper VS ON etc what do you intend to achieve? The PDP may glow (if the control board works), but will still not display any image, because the main board will not be sending it one.

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

I don't think so; why do you think that will work?

It looks to me like your main board has a problem meaning it won't power up for some reason or another.

Even if you do jumper VS ON etc what do you intend to achieve? The PDP may glow (if the control board works), but will still not display any image, because the main board will not be sending it one.

I am thinking that the main board might be OK as it is working to the point when it sends voltage through RL ON which I presume is then triggering the relays on the power supply to feed 5V MONI back to the main board BUT that is not happening ???
Plus I bought a new main board from Holland and it does the same ???
Like I say I am clutching at straws and am reading as much as I can about it and this is where I have ended up ???

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

Unfortunately a great deal of these problems are down to firmware/software problems with the main board -- some part of the firmware gets corrupted, or some anomalous condition occurs, which means that it never completes boot-up. It's like a computer, the main board, except you can't replace most of the parts. Parts from used TVs can be defective, too, so don't rule out a bad part being received.

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

Unfortunately a great deal of these problems are down to firmware/software problems with the main board -- some part of the firmware gets corrupted, or some anomalous condition occurs, which means that it never completes boot-up. It's like a computer, the main board, except you can't replace most of the parts. Parts from used TVs can be defective, too, so don't rule out a bad part being received.

OK thanks ... I am in the process of sourcing a service manual for it ??

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

These close enough?

http://elektrotanya.com/lg_50px4r.djvu/download.html

djvu reader needed for the 2nd one.

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

These close enough?

http://elektrotanya.com/lg_50px4r.djvu/download.html

djvu reader needed for the 2nd one.

Thanks Tom that's great !!! I did manage to find a service manual before for LG50PX4R But it did not have as much information as the different one !
I will give these a good read today and hopefully might be ablt to get somewhere

I know that the main board is like a computer but on the previous LG50pq30 manual it mentions about force starting the power sequence ?? by inserting 100 ohm resistors ??? Ive attached the page where it says it ??? Do you think its worth a try before I scrap the TV????

Thanks again

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

The force starting procedure is only used to get the power supply to fire up; not to get the TV to work. By force starting it, you can see if the voltages Vs, Va etc come up.