LG 42LZ30 won't power up

[DSham]

Hello all,
I'm new here and need some help. Has anyone had any experience with this model? The STBY voltage is not 6 volts. Its goes up and down 3v-5.8v

Does anyone know which capacitor is the startup voltage? I have tested voltages/caps an changed a few caps with no success. Any help is appreciated.

[dick_barton]

Re: LG 42LZ30 won't power up

Would you like to post clear sharp photo's of your circuit boards as a good starting point when seeking help.

[DSham]

Re: LG 42LZ30 won't power up

Sorry about that. Here it is. The part number is visible also. The voltage across the bridge rectifier is good. The high voltage Caps are good as well.

[dick_barton]

Re: LG 42LZ30 won't power up

You have a number of white connectors running along one edge of the board. Alongside each pin of the connectors there is a printed label,.

Can you measure the voltage on each pin and give the name and voltage read for each of the pins. That will help to identify where the fault is.

[DSham]

Re: LG 42LZ30 won't power up

I wrote these down as they are shown in the pic. I separated the connectors by spaces

6VST=0V
GND
PIN (WITH NO NAME)=0V
TX=.037V
RX=.002V
GND
IR-LINE=0V
IR-SEL=0V
GND


18V/2.3A=0V
GND


33V/.1A=0V
33V/.1A=0V
GND
6V/2A=0V
6V/2A=0V
GND
GND
3.4/2A=0V
3.4/2A=0V
GND
3.4VSB=3.3V-3.4V (But pretty stable)
18V/2.3A=.025 (Dropped down to.001v)
GND
6VSB=3.9-5.9 (Very unstable)


INV=0V
BRI=0V
PWR ON/OFF1=0V
PWR ON/OFF2=.999-5V (VERY UNSTABLE)
GND


24V/10A=0V
24V/10A=0V
GND
NC
15V/1A=0V
GND
6V/2A=0V
3.4V/2A=0V
GND
6V-SB=3.9-5.3V (VERY UNSTABLE)
33V/.1A=.002V
BRI=0V
INV=0V
PWR ON/OFF1=0V
PWR ON/OFF2=.999-5V (VERY UNSTABLE)


24V/10A=0V


24V/10A=0V

[dick_barton]

Re: LG 42LZ30 won't power up

I'm not familiar with the set but it appears to have two standby voltages3.4V & 6V
The 3.4V looks fine but you need to find out what the fault is with the 6V standby voltage. Once you have that back and stable I think you could then progress looking to see if there is any other problem.
Have you got the power supply schematic? A good search of the internet wouldn't do you any harm and would be useful if you could find it.

[DSham]

Re: LG 42LZ30 won't power up

I have the service manual but it does not show the power supply.

I took a reading off 2 ceramic capacitors. The numbers printed on them are
"B471k 1KV"

this is a 470nF correct? I took it out of circuit and it measures 0.889nF.

Could this be the issue or did I read the cap wrong? It's been a while since Ive troubleshot down to component level so I'm rusty.

[ReeceyBurger123]

Re: LG 42LZ30 won't power up

Try heating the Psu see if it comes on. Common issue on these is bad 47uf caps on the primary side.

[dick_barton]

Re: LG 42LZ30 won't power up

Without the schematic I can't really say what is wrong other than there is a problem with the 6VSTB supply.
Do any of the electrolytic capacitors have domed tops (rounding). Using a multimeter have you checked the diodes?
What are the numbers on the 4 off IC alongside CON803. The IC next to D581 looks broken?

[ReeceyBurger123]

Re: LG 42LZ30 won't power up

Mainly heat the area I have screen shot:

[DSham]

Re: LG 42LZ30 won't power up

So I finally got back up and running. I believe it was the 47uf caps but I'm not 100% sure. I removed them, took readings and one of them was suspect so I replaced them all as well as most of the medium to small caps on the board I questioned. $11.00 investment. Can't beat that. Thanks for the help guys.