LG 42lv42700

[wazzadj@hotmail.com]

Hi Guys ,
i have a LG 42inch LED tv 42LS5700 come into the shop
SYMptoms wont turn on Flashing LED standby light 2 fLASHESS then off Cycles
NO PIC No SOUND NO BACKLIGHT
responds to Remote control to turn on From solid red stanby but then 2 red flashes on led light standby

Ok so i have found the following issues
Blown output regulators on PSU board - decided all to hard to fix and replaced whole PSU board refurb /secondhand EBAY

plugged in replacement board Still have same Fault
so checked following on PSU Main Connector to MB

Voltages at PSU are as follows\
all voltages are there except PO/on pin 1. Blue wire in connector Should be seeing 3.5v standby meter on Grnd chasis Postive red probe PIN 1 on PSU connector i get (0v) with set turned on tried pulling up with 3.5v no response
i have my 12v 24v & 3.5v lines in the rest of plug
I have 48vdc at TP210 LED +
seems a little low to me ? i would of thought i would be seeing around 70VDC
I believe i am not getting a Output from MB IC or i Have a shorted LED circuit pulling down (still have to investigate that)
Possibly no Signal from MB IC P/on DRV ?
I have even tried heating up MB main Chip for BG issue ?
I have Hestitantly ruled out the PSU board cause SUpposably its been tested to Work? lol with fingers crossed !
I have tried disconnecting LED Cable at top of PSU p210 connector STill no 3.5v on P/on
Is there a way to force the PSU to turn on say 3.5vdc Pon & BL/on ?

ANy suggestions where to look help much appreciated
cheers
Wayne

[budm]

Re: LG 42lv42700

Can we see good clear straight shot pictures of the power supply board and also the pictures of the power supply board connector that goes to the main board? That way we can easily see the labels for each pin because your pin description is not very clear to me.

[wazzadj@hotmail.com]

Re: LG 42lv42700

Sure Will do when i get back into shop will upload for you thank you so much for your help
cheers
Wayne

[budm]

Re: LG 42lv42700

We also need the pictures of the whole backside of the TV showing all the boards.

[dick_barton]

Re: LG 42lv42700

Some power supplies will bring up the backlights when powered up when disconnected from the mainboard.
Otherwise with the mainboard still disconnected jump standby voltage to BL_ON using a 1K resistor and a second 1K resistor jump standby voltage to Pon.

Pictures are generally helpful as Budm has suggested not having the set in front of us.

[Andrew F. Ali]

Re: LG 42lv42700

That sounds like a Main Bd issue. I had a LG showing similar symptom. It was easier for me to replace the Main Bd. Set worked with a new board. I did not investigate the old board to pin point the faulty component as replacement was the more cost effective option for me.

[Ollyb45]

Re: LG 42lv42700

Back in the shop and am including pic's of the boards as requested. Have included the pics in segments so visibility will be accessible.

[wazzadj@hotmail.com]

Re: LG 42lv42700

Back in the shop and am including pic's of the boards as requested. Have included the pics in segments so visibility will be accessible.

Model is LG 42 LS5700

[wazzadj@hotmail.com]

Re: LG42 LS5700

Hi Guys , thankyou for your kind assistance as per requested please find attached pictures of the rear of tv and the boards in question
please refer to previous posts on issue with Standby power supply circuit not switching on the tv
Have checked the Main PSU board connector {P201)
have the following voltages on the following pins
Note pin 1 is the blue wire bottom to top (pin 12) of connector on back of connector
Sorry dont have voltages on bottom of board at this time

(48v ) LED +v
320v Supply cap


1. PO (800mv)
2.(24v)
3.Gnd
4.Gnd
5.(3.5v)
6.(3.5v)
7.Gnd
8.Gnd
9.(12v)
10.(12V)
11.(12V)
12.pwR dIM (0V)

cheers
Wayne

[attainteddragon]

Re: LG 42lv42700

when you list voltages, list all pins. in this case the top row is most likely the odd pins and the bottom row the even. you can probe through the connector where the wire enters it. then report the voltages as,
pin desc, v in stby, v when power switch is activated.

if your 3.5 stby voltage is present, is power on rising above 2v when you press the power button? if not, then your issue is on the main board.

[budm]

Re: LG 42lv42700

Per picture,
Pin 1 is the PWR-ON PIN, not PO. that is the PS-ON pin.
Pin 3 = 24V
Pin 5 = GND
Pin 7 = GND
.....
.....
The exposed pins that you can see from the top side board are ODD number pin, the EVEN number pins, you will have to use probe with skinny tip to probe from the back side of the connector where the wires go in.
If you are getting the switched 24V and switched 12V then the PS-ON is working, but at this point we need the Voltages of ALL the pins.

[budm]

Re: LG 42lv42700

Where are the pictures requested in post #4?

[wazzadj@hotmail.com]

Re: LG 42lv42700

Ok i tested the {PSU plug today P201 , here is the voltages on the pins as requested please find attached diagram

Cheers
Wayne

[Andrew F. Ali]

Re: LG 42lv42700

Where are the pictures requested in post #4?

Bear in mind that we do not have your TV in front of us and without the pictures requested we will be unsure regardless of how much information you give us.

[attainteddragon]

Re: LG 42lv42700

Some power supplies will bring up the backlights when powered up when disconnected from the mainboard.
Otherwise with the mainboard still disconnected jump standby voltage to BL_ON using a 1K resistor and a second 1K resistor jump standby voltage to Pon.

this would be my next step.

from what you have written, it looks to me like the main is faulty.

[wazzadj@hotmail.com]

Re: LG 42LV5700

Please find attached Photos as requested
ON a NOTE i have noticed a discoloured brown area on the top of the back of Panel and all so under the PSU board where it is mounted
Could this have been a possible liquid spilled in to it EG COFFEE STAIN view Photo zoom in or is it just Burn hot area from board

Ok so did some more test found that PWR-on pin 1 on PSU board connector
has no 3.5v getting 0V
I am getting all my other voltages 24v 12v 3.5v on connector
tried jumping from 3.5v on connector no stndby turn on 0v on meter
should it have fired up the supply or is ot being held down in protection due to a detected short in the LED board or the MAIN cPU on the main board?

i have not dismantled the front of panel and had a look at LED assy yet
wanted to see what you guys think, i dont want to order MAIN BOARD in case the board is being shut down in protection from a faulty LED circuit
any suggestions please what to test next ?
OH by the way i have 47vDC at TP LED+ on PSU board where the LED panel connects
cheers
Wayne

[attainteddragon]

Re: LG 42lv42700

right now your main is not working properly. no ps/on signal.

to jump the power supply on, you will need to jump pin 1 (ps/on) to one of the 3.5v stby rails and jump pin 18 (drv-on) to a 3.5 stby rail. also disconnect the harness that goes from the ps to the main. if you disconnect it from the main, you can then use the loom to insert your 1k jumping resistors.

[wazzadj@hotmail.com]

Re: LG 42lv42700

Thanks attainteddragon
will give it a go and post back results

cheers
Wayne

[wazzadj@hotmail.com]

Re: LG 42lv42700

Ok Guys back with the results of testing the PS turning on when jumping
pin 1. (3.5v pw-on) & pin.18 (3.5v Drv-on)

he backlight turns on the PSU fires up ok
so looks like the Main Board is in question is the Fault not outputting the 3.5v from main board processor to PSU
Time to tell customer to hand over more money lol

Hey guys thanks for your help
Cheers
Wayne

[Andrew F. Ali]

Re: LG 42lv42700

Post#6 already earlier advised the Main Bd as the issue.