LG 42LW4500 no power

[spintop]

My LG 42LW4500 no power at all, no led lights. First suspect is power board issue. All fuses are OK, AC voltages are going into the board. ac voltages did not reach the rectifier. And cannot detect ac voltage after the relay.
I cannot find the board schematic on web. So cannot see where n how to turn on the relay.

Power board - EAX62865401/8
4 pins Relay is 12V - F3PA012V (yellow circle in pic)

any help from the experts, will be appreciated.
thanks !

[spintop]

Re: LG 42LW4500 no power

Find from the web, this board should give 3.5v standby before bridge rectifier receive the ac voltage. The relay device control this. When tv is switch on, control signal trigger the relay to activate "click" sound n rectifier starts. the rest of power voltage is produced.

In my case, I don't get 3.5v n no click. No 3.5v means nothing works. I trace to a PWM ic A6095H (at bottom right) 8 pin. Suspect it could be faulty. Still sourcing for ic.

Anyone know how to confirm IC is dead.

[budm]

Re: LG 42LW4500 no power

The main board will send out PS-ON signal when power switch is activated to turn on the power relay.
Please list the pin names and the DCV reading of each pin of the connector of the power supply board that goes to the main board, the readings will be when TV is plugged in but not turned on and then after the power switch is activated so we can see what is/are missing.

[fredaelsadany]

Re: LG 42LW4500 no power

HI
Please take voltages on socket ps to the MB .
and tell us about hearing the relay click if happend it means MB proccesor is acting .
if nothing happened please be sure of stand by voltage (+5v ) .
then measure regulators in the pic below . tell us what happened .
service manual also found .
thanks

[spintop]

Re: LG 42LW4500 no power

The main board will send out PS-ON signal when power switch is activated to turn on the power relay.
Please list the pin names and the DCV reading of each pin of the connector of the power supply board that goes to the main board, the readings will be when TV is plugged in but not turned on and then after the power switch is activated so we can see what is/are missing.

pin labels here
nc error
12v pwm
12v nc
12v drv-on
gnd vsys
gnd gnd
3.5v 3.5v
3.5v 3.5v
gnd gnd
gnd gnd
24v 24v
pwr-on 24v

all pins are 0v, both before or after on

The reason is because the ac voltages did not reach the bridge rectifier stage so no power voltages are generated. ac voltage going to brigde rectifier is controlled by the relay before it. from tracing, I believe the relay is dependent on 3.5v standby and pwr-on from the main board when tv is turn ON. in my case, i dont even have 3.5v, from which i suspect the ic A6095h to be faulty.

[spintop]

Re: LG 42LW4500 no power

HI
Please take voltages on socket ps to the MB .
and tell us about hearing the relay click if happend it means MB proccesor is acting .
if nothing happened please be sure of stand by voltage (+5v ) .
then measure regulators in the pic below . tell us what happened .
service manual also found .
thanks

thanks for the pdf.
but it only have diagrams for the main board, they didnt provide the power supply board diagram.

No click and no 3.5v

[fredaelsadany]

Re: LG 42LW4500 no power

HALLO
here is the stand by circuit on the output two diodes measure 5v if not found the whole stand by cir not working ( that means IC/ CONDENCERS/NO DC ON IC/OPEN RESISTOR...) .
IF VOLTAGE OK ON THE DIODES FROM THE DIODES TO POWER SUPPLY SOKET MEASURE THE PATH .
THANKS

[budm]

Re: LG 42LW4500 no power

At the bottom right of your picture where the standby power supply is, there is a fuse and two main AC filter for the STBY SMPS IC.
The fuse is good and you do have DCV bwteen the two legs of those two filter caps for the STBY supply?

[Diah]

Re: LG 42LW4500 no power

Anyone know how to confirm IC is dead.

first things of all sudden trouble you wrote here, this LG Power board will never turn on if you had disconnected Backlight sockets. either firmware will boot with error to turn of PWB.

second. follow budm to get hand on the standby volts.

[fredaelsadany]

Re: LG 42LW4500 no power

Hallo
here is what the company siad in her chart .
please say what is the voltage on the diodes out to the stand by chopper !!
if no voltage your work in the stand by cir no software now . this voltage first .
here some of the company explain .
try with it
thank you

[spintop]

Re: LG 42LW4500 no power

everyone thanks for the suggestions.
these are voltages on the standby circuit sides, in the picture.
DC voltage taken against the hot side ground. except the 2 big diodes on the sec side.

[budm]

Re: LG 42LW4500 no power

Can you please verify the P/N as printed on top of that SMPS IC? A6095 does not come up with anything with SMPS.
All the numbers as printed on top of the IC. Or good closed up pictures.
Those two rectifiers D201, 202 are OK?

[spintop]

Re: LG 42LW4500 no power

Can you please verify the P/N as printed on top of that SMPS IC? A6095 does not come up with anything with SMPS.
All the numbers as printed on top of the IC. Or good closed up pictures.
Those two rectifiers D201, 202 are OK?

my mistake, typo error - its A6059h.

i pull out the 2 big diodes, they are 2 different marking. what is the difference ?
Diode 1) -SB560 SSG11033 - shorted
Diode 2) -SB560 SSG11022 - ok

intend to replace them.

[budm]

Re: LG 42LW4500 no power

Those two diodes are the same, SB560, they are connected in parallel so when you tested them while they are still soldered to the board, if one is shorted out then both of them should show as shorted circuit. You should remove them and retest, if one is shorted out then I would replace both of them.

[spintop]

Re: LG 42LW4500 no power

yes indeed, have pulled them out of circuit, one shorted.
i was wondering why marking is different. will see if i can get some from local store.
hopefully i can get back the 3.5v

will update later, thanks all

[budm]

Re: LG 42LW4500 no power

The other numbers may be for date code, factory code, etc.

[spintop]

Re: LG 42LW4500 no power

success !!
replaced 2 diodes, got the power led light, switch on can hear the click sound.
tv up and running.

Thanks budm and everyone who have offered suggestions and information.

[budm]

Re: LG 42LW4500 no power

Thanks for the repair follow-up.

[edwardlau]

Re: LG 42LW4500 no power

Hi all,
If the measured reading as attached. What fault should be?

Thank

[budm]

Re: LG 42LW4500 no power

What did you use for GND? You are working on the primary side of the circuit so the black probe should go to the negative leg of either one of the main filter cap.
You country Voltage is 220VAC?
So if you check the resistance (no power applied to the board) of those two barrel diodes (the two that you show 0V reading) in the cold side, what resistance do you get.