LG 42LW4500-LB Need help with repair of PSU

[UndeadLuke]

Hi guys today my TV stops working (it woudnt turn on only led shine so the power goes into it) so i remove the back panel and unscrewed the PSU I checked the capacitors but all of them seems to bee good psychicaly I dont check their capacity if its good or not because no one of them is leaked after that i check whole board with my multimeter (PAN33D) and i found 2. suspicious components (it was thermistor) when i put + and - of my multimeter on it and multimeter was set to beep when he found short-circuit it beeps so I dissolder this 2 thermistors and do it again i again put + and - of my multimeter on their poles and it against beep so i think my TV wasnt start because this thermistors are in short-circuit (i read thermistor is for protecting whole board from short-circuit) So please can you help me ? I also need buy new but my local store doesnt have this one (I put photo in attach smaller one had DSC10D-9 printed on it and the bigger one had DSC-5D-15 120) if you dont understand me i will record a video on Youtube.Thanks for help

[ReeceyBurger123]

Re: LG 42LW4500-LB Need help with repair of PSU

Thermistors should show short or low ohms, what voltage have you got on the main filter caps ?

[dick_barton]

Re: LG 42LW4500-LB Need help with repair of PSU

They are probably OK. Measure their ohmic value.

[dick_barton]

Re: LG 42LW4500-LB Need help with repair of PSU

There are a number of fuses on the board which you have checked and were OK?
What dc voltages do you have across the 2 legs of each of the 3 long capacitors.

[UndeadLuke]

Re: LG 42LW4500-LB Need help with repair of PSU

Thermistors should show short or low ohms, what voltage have you got on the main filter caps ?

Okey so thermistors are good if they signal short ? I dont know what is main filter cap on this board but I think it is the gray one (photo in attach) also how can i find the voltage without put in in my 230v plug ? Iam noob in this hte black thing under the gray capacitor is 230v plug

[UndeadLuke]

Re: LG 42LW4500-LB Need help with repair of PSU

They are probably OK. Measure their ohmic value.

Ok I will solder them back

[ReeceyBurger123]

Re: LG 42LW4500-LB Need help with repair of PSU

Check the forum using the search feature on how to test Psu.

[UndeadLuke]

Re: LG 42LW4500-LB Need help with repair of PSU

There are a number of fuses on the board which you have checked and were OK?
What dc voltages do you have across the 2 legs of each of the 3 long capacitors.

I cant check the voltage of the 3 long capacitors with power on because my multimeter support only 230volts but the capacitors had 450v

[dick_barton]

Re: LG 42LW4500-LB Need help with repair of PSU

The attached picture looks like your power supply and if from an LG-47LW5700 model.
Can you check you have the voltages shown in the table.

[UndeadLuke]

Re: LG 42LW4500-LB Need help with repair of PSU

The attached picture looks like your power supply and if from an LG-47LW5700 model.
Can you check you have the voltages shown in the table.

Yes I can but before I will return the thermistors also must i plug the 230v in it ? i had the down model of board so i will check it but i think the leds work because my tv turn on for second and then turn of like she found short circuit

[dick_barton]

Re: LG 42LW4500-LB Need help with repair of PSU

It's very likely the set has powered down because there is a fault, however that is what you are trying to find. Nothing is blowing up or burning.

You really need a meter that has a 600V DC range to test that the mains supply is being rectified and is reaching the higher voltage parts of the circuits. For example to find out if you have 400V on those capacitors.

[UndeadLuke]

Re: LG 42LW4500-LB Need help with repair of PSU

It's very likely the set has powered down because there is a fault, however that is what you are trying to find. Nothing is blowing up or burning.

You really need a meter that has a 600V DC range to test that the mains supply is being rectified and is reaching the higher voltage parts of the circuits. For example to find out if you have 400V on those capacitors.

Okey but I dont understand why they put higher voltage capacitors than it came to board they are dimensed to 470v nothing in my country has 450v maximal range from plug is 380v i will wait 2 days until my school starts and i will ask my teacher for help to find the problem i returned the thermistors do you think it helps when i bought new capacitors and replace them ?

[dick_barton]

Re: LG 42LW4500-LB Need help with repair of PSU

The incoming mains of 230v ac is rectified to produce DC and then that DC voltage is increased by the circuit to approximately 380 - 400V DC.
There is no point in changing anything until you find that it is faulty!!!

[UndeadLuke]

Re: LG 42LW4500-LB Need help with repair of PSU

The incoming mains of 230v ac is rectified to produce DC and then that DC voltage is increased by the circuit to approximately 380 - 400V DC.
There is no point in changing anything until you find that it is faulty!!!

Ah okey thanks I wil try check it with my teacher but also i found something this board has 2 circuit primary and secondary and i cant measure ohms on resistors on second circuit thats weird on first sector of board theres no problem with measure ohms on resistor

[UndeadLuke]

Re: LG 42LW4500-LB Need help with repair of PSU

I will wait 2 days and try to find the problem with my teacher of electrotechnics

[dick_barton]

Re: LG 42LW4500-LB Need help with repair of PSU

To start off, what is the DC voltage across those capacitors. See post #11

[UndeadLuke]

Re: LG 42LW4500-LB Need help with repair of PSU

Okey guys So I make big progresws today I check the big capacitors and no voltage on them the voltage stops on part INR or LNR next to main gray CAP so this part is definitly damaged does anyone know which one i need to replace ? it looks like Varistor but i dont know nothing about it

[budm]

Re: LG 42LW4500-LB Need help with repair of PSU

https://www.badcaps.net/forum/attach...7&d=1479570017

So the fuse to left of the line filter cap (grey cap) is good for sure?
Are you getting 230VAC between the two legs of that grey cap?

[UndeadLuke]

Re: LG 42LW4500-LB Need help with repair of PSU

https://www.badcaps.net/forum/attach...7&d=1479570017

So the fuse to left of the line filter cap (grey cap) is good for sure?
Are you getting 230VAC between the two legs of that grey cap?

Yes 250VAC on gray cap on right side of it its some type of varistor or part (i dont know what it is and which one i need to replace) this part has voltage on + but if you try + and - no voltage everything after that it has no or bad voltage in miliamperes

[budm]

Re: LG 42LW4500-LB Need help with repair of PSU

We need clear straight shot pictures of the whole board.
There is a bridge rectifier (4-pin black device) mounted on the heatsink, you need to check the ACV between the two inner legs, it should have 230VAC between those two legs.
https://www.badcaps.net/forum/attach...8&d=1479570017