LG42LT360c won't turn on, power on voltage question.

[Azza111111]

Hi guys,

Got the above tv but can't turn it on.

I have a standby light but when powered on the standby light just flashes twice.

The primary part of the power board is hot ie powered up with 400v+ and 230v+ but only 3.5v max on the cold side.

I wanted to check if power on voltage was present, blue wire in picture but it says 24v? I get 3.5 when I power on.

Should it be 24v as depicted in the legend? And does that hint at a main board fault?

Thanks

[Azza111111]

Re: LG42LT360c won't turn on, power on voltage question.

Ah...Just checked all pins on that plug and I get 3.5v on the power on and no 24v anywhere just 3.5v or less.

I looked at this little transformer, I have 400v on one side and nothing coming out the other side so could be a suspect? Or is it waiting for a signal to turn on?

[dick_barton]

Re: LG42LT360c won't turn on, power on voltage question.

You may have to take the 3.5V and connect to Power_ON using a 1K resistor to check the other voltages. Done with the mainboard disconnected.

[Azza111111]

Re: LG42LT360c won't turn on, power on voltage question.

You may have to take the 3.5V and connect to Power_ON using a 1K resistor to check the other voltages. Done with the mainboard disconnected.

Sorry took me ages to get an hour or so to try this.

Ok so I connected 3.5v via a 1k resistor to power on, still go no voltages on any pins other than the 3.5v pins checked I had voltage at the power on pin so this was OK.

I took out the bridge rectifier and tested it and that tests good.

I noticed I have a slightly unstable voltage of 350-375v on the hot side of the board at various points?

[budm]

Re: LG42LT360c won't turn on, power on voltage question.

How about good clear straight shot pictures of the power supply board top and bottom side?
Board P/N EAY?????, EAX???????

https://www.badcaps.net/forum/attach...2&d=1476517630
That little transformer is for the Standby power supply and it is working because you are getting the 3.5VDC.
BTW, when you were checking the Voltages on the HOT side, what did you use for e GND for the meter, chassis?

[Azza111111]

Re: LG42LT360c won't turn on, power on voltage question.

How about good clear straight shot pictures of the power supply board top and bottom side?
Board P/N EAY?????, EAX???????

https://www.badcaps.net/forum/attach...2&d=1476517630
That little transformer is for the Standby power supply and it is working because you are getting the 3.5VDC.
BTW, when you were checking the Voltages on the HOT side, what did you use for e GND for the meter, chassis?

Hi here's the top side photo, I will get the bottom side tomorrow, yeah chassis as ground.

I'm learning with all this but am really interested in leaning new things in electronics so please Bare with with me!!

[budm]

Re: LG42LT360c won't turn on, power on voltage question.

When you work in the primary side of the circuit, you will use the negative leg o the main filter cap as the GND ref. for the meter, you can use the chassis as the GND ref. when you working in the secondary (cold) side of the circuit.

[Azza111111]

Re: LG42LT360c won't turn on, power on voltage question.

When you work in the primary side of the circuit, you will use the negative leg o the main filter cap as the GND ref. for the meter, you can use the chassis as the GND ref. when you working in the secondary (cold) side of the circuit.

Great thanks for the tip, I will re test later just in case I've missed something.

[Azza111111]

Re: LG42LT360c won't turn on, power on voltage question.

Here's the photo of the rear of the board, please excuse the messy soldering in places I intend to tidy up after I've finished and return that diode to the other side 😕

[dick_barton]

Re: LG42LT360c won't turn on, power on voltage question.

Have you checked that both fuses are OK. What is the DC voltage across the two legs of the marked capacitor
1) in standby
2) when you connect 3.5V to Power On using the 1K resistor

[Azza111111]

Re: LG42LT360c won't turn on, power on voltage question.

Have you checked that both fuses are OK. What is the DC voltage across the two legs of the marked capacitor
1) in standby
2) when you connect 3.5V to Power On using the 1K resistor

Thanks for the info sorry for the late reply been away a lot with work, across the 450v capacitor I'm getting 400v I've checked the fuses for continuity and checked both sides for voltage so these should be ok?

[dick_barton]

Re: LG42LT360c won't turn on, power on voltage question.

What are the voltages corresponding to all the connector pins as shown in the legend highlighted in orange.

[Azza111111]

Re: LG42LT360c won't turn on, power on voltage question.

That's the strange thing, I get 3.5v on the 3.5v pins but nothing on any other and I've just double checked that.

[dick_barton]

Re: LG42LT360c won't turn on, power on voltage question.

So you have 0V on ALL the other pins on that connector and only 3.5V on the pin marked 3.5V. Is that correct? And is this with or without the main board connected to the power supply?

[dick_barton]

Re: LG42LT360c won't turn on, power on voltage question.

I wanted to check if power on voltage was present, blue wire in picture but it says 24v? I get 3.5 when I power on.

The blue wire looks as though it goes to Pin_1 which is Power_On so 3.5V would be coming from the main board to turn on the set. You can check this by switching the set into standby and monitoring the voltage on the blue wire.

[Azza111111]

Re: LG42LT360c won't turn on, power on voltage question.

That's with the main board disconnected but the resistor from 3.5v to power on. The main board when connected does put 3.5v on to Power_ON on the blue wire.

[budm]

Re: LG42LT360c won't turn on, power on voltage question.

So the PFC Voltage booster is working.
How about the fuse right next to the main filter cap, is it OK?
That fuse takes the Boosted Voltage from the main cap to feed the switched SMPS power supply that supplies all other Voltages to the main board and to the LED backlights circuits.
If the fuse is OK, then you need to check the capacitance that rectangular grey coupling cap C114 (to the right of the fuse) to see if its capacitance is still within the tolerance or not.

LG EAY62789601 Power Supply
PCB# 3PAGC10096B-R
http://www.shopjimmy.com/lg-eay62789...-led-board.htm

[Azza111111]

Re: LG42LT360c won't turn on, power on voltage question.

So the PFC Voltage booster is working.
How about the fuse right next to the main filter cap, is it OK?
That fuse takes the Boosted Voltage from the main cap to feed the switched SMPS power supply that supplies all other Voltages to the main board and to the LED backlights circuits.
If the fuse is OK, then you need to check the capacitance that rectangular grey coupling cap C114 (to the right of the fuse) to see if its capacitance is still within the tolerance or not.

LG EAY62789601 Power Supply
PCB# 3PAGC10096B-R
http://www.shopjimmy.com/lg-eay62789...-led-board.htm

Thanks, the fuse is good I get equal voltage both sides, I will check out that cap!!

[budm]

Re: LG42LT360c won't turn on, power on voltage question.

If the cap is tested OK then the next thing we will need is the P/N of that 18-pin SMPS IC.
https://www.badcaps.net/forum/attach...2&d=1477039653

[Azza111111]

Re: LG42LT360c won't turn on, power on voltage question.

If the cap is tested OK then the next thing we will need is the P/N of that 18-pin SMPS IC.
https://www.badcaps.net/forum/attach...2&d=1477039653

Thank you guys sooooo much, finally got round to testing,searching and buying/replacing the grey capacitor and put board back into tv and to my shock it fired up!!!

Thank God it was the cap as I don't know what a SMPS is!!!

Thanks again for this