LG 50PX4R-ZB stuck in standby mode

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

Hi again !!

I cannot send the main board back so i am going to try and sell it on ebay !! I was then going to buy a power supply board for it ?

Thanks Tw for the protection mode diagram. I will test it out tommorow after work.

The TV defenitely makes a click sound when first turned on just before it goes back to standby, however if i turn it on again by the remote it does NOT click. It only clicks when i unplug the tv and plug back in ??

Thanks again for your help

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

Tom, this set appears to use the same ysus,zsus as the 50PX5D. I'd have a closer look for shorts, blown fuses or symptoms on those boards and IPMs.

The initial post symptoms sounds like it could be protection mode. I don't remember all the ins and outs of the couple I had but sounds similar and I know on those you'd get a click , LED would change then back to standby in about 10secs.

IPMs replaced on both Y & Z got that junker going again and a bad Ysus was burning up resistors on the Z.
Horrible TVs to work on, the LG Fallas TV trainig guide would be close to this, but the translation to english makes the flow charts near impossible to understand.

There's a note , Unable to check voltage when disconnecting Ysus due to 50" protection?

Hello Thanks for trying to help me out with my TV problem..... I have done some continuity testing on the power board and ysus and zsus.( not switched on !)
I might be totally wrong BUT i am thinking it is the YSUS board ???? The reason i say this is because i have continuity between grounds and all the vs+ on the YSUS board with the power leads and zsus lead disconnected.
Have i got a short somewhere between ground and VS+ and where do you think the fault could lie ????
Thanks steve

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

Hello Thanks for trying to help me out with my TV problem..... I have done some continuity testing on the power board and ysus and zsus.( not switched on !)
I might be totally wrong BUT i am thinking it is the YSUS board ???? The reason i say this is because i have continuity between grounds and all the vs+ on the YSUS board with the power leads and zsus lead disconnected.
Have i got a short somewhere between ground and VS+ and where do you think the fault could lie ????
Thanks steve

Forgot to mention the resistance between ground and VS+ is 130 ohms

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

Hi

I think i am miles away with finding out the cause of this fault ???

I just took the fuses out of the ysus board and GND and VS+ dont show continuity , so i am presuming it is normal.
I checked the continuity between GND and VS on the power board and they also have continuity so i presume these are normal ?
On the diagram TW attached it says to take out connectors P800, P802 and P803 on the power board.
P800 is on the main av board and there is nothing connected in P803 ???
Anyway i disconnected P800 and P802 and when powered up the TV does not turn on JUST the red light and thats it ????
Thanks for any help

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

Fuses SHOULD show continuity, your reading is not normal.

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

Fuses SHOULD show continuity, your reading is not normal.

Hi tom

the fuses read 000.3 ohms

the continuity between gnd and vs reads 130 ohms with fuses in

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

OK GND-Vs continuity that low is bad. So you may have bad IPM or another fault on sus board.

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

OK GND-Vs continuity that low is bad. So you may have bad IPM or another fault on sus board.

Are there any checks i can do to try and determine the fault ??

Could it be YSUS or ZSUS or both ??

thanks

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

Is GND-Vs measured like that on both Y-sus and Z-sus?

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

Is GND-Vs measured like that on both Y-sus and Z-sus?

GND & Vs = 5.4 K ohms on ZSUS
GND & Vs = 0.120 K ohms on YSUS

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

If you reverse the probes on each board, what do you read? Is it any different?

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

If you reverse the probes on each board, what do you read? Is it any different?

ZSUS
BLACK PROBE ON CHASSIS & RED PROBE ON VS = 4.2 M ohms

RED PROBE ON CHASSIS & BLACK PROBE ON VS = 5.4 K ohms

YSUS
NOTHING CHANGES STILL 130 ohms

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

OK, your Y-sus is bad, and your Z-sus appears OK.
Troubleshooting I do not know much but try narrowing down the short by removing parts one at a time, I suspect the IPM is at fault which is difficult to isolate.

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

OK, your Y-sus is bad, and your Z-sus appears OK.
Troubleshooting I do not know much but try narrowing down the short by removing parts one at a time, I suspect the IPM is at fault which is difficult to isolate.

Thanks tom .. where is the IPM ??

when you say removing parts do you mean connection leads ? Could it be a bad capacitor even though i cant see anything unusual ?? there is some big caps that dont look perfectly flat on the top ??

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

The capacitors on these boards usually aren't perfectly flat, this isn't a sign of a failed cap.
IPM is under the largest heatsink on the board.
Narrowing down the fault on these boards is very difficult due to the multi-pin connections used on the sub-modules and IPM modules.

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

The capacitors on these boards usually aren't perfectly flat, this isn't a sign of a failed cap.
IPM is under the largest heatsink on the board.
Narrowing down the fault on these boards is very difficult due to the multi-pin connections used on the sub-modules and IPM modules.

OK thanks tom, basically i need a new YSUS board ?
Is it true that i would probably also need the Y upper and Y lower buffers ?

Because it is a short between GND and Vs do you think there is a good chance it could be a diode ? its just something i read on an ebay YSUS repair kit ... it says a diode under the big heatsink can short on the ysus board ?

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

OK, your Y-sus is bad, and your Z-sus appears OK.
Troubleshooting I do not know much but try narrowing down the short by removing parts one at a time, I suspect the IPM is at fault which is difficult to isolate.

I have taken off the YSUS board and have taken some pictures of the rear of the board. Ive noticed some brown marks/stains? Do you know what this could be from ??

thanks

[tom66]

Re: LG 50PX4R-ZB stuck in standby mode

It's flux residue.
You can check your buffers for shorts
http://blog.coppelltvrepair.com/2010...er-boards.html

I do not know if a diode could cause this, I don't work on these sets due to all of the IPM problems they have which make them very difficult to repair.

[surferbum]

Re: LG 50PX4R-ZB stuck in standby mode

OK, your Y-sus is bad, and your Z-sus appears OK.
Troubleshooting I do not know much but try narrowing down the short by removing parts one at a time, I suspect the IPM is at fault which is difficult to isolate.

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

[tom66]

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.