Lg 42pq3000 dead

[karlpowell]

As above lg 42PQ3000 totally dead , no led lights , I have swapped the power board as I had 1 spare, but the fault is still there

when i power up the set i get 0V on all pins from the from the power supply to the main board (i have checked all fuses on the power supply and checked that 240v in is OK i have unplugged the sustain boards and still get the exact same fault .

any ideas guys

[ReeceyBurger123]

Re: Lg 42pq3000 dead

Check the Diode on the 5vstby rail.

[tonydix]

Re: Lg 42pq3000 dead

Please can you be more specific. Is the diode on the power board or on the control board ?
I have an interesting situation where 5vstby is up when the control board is unpluged but is lost 1 sec after reconnecting. Presumably a safe shutdown proceedure. Many thanks.
Tony

[Biruslapio]

Re: Lg 42pq3000 dead

Do not plug the mainboard on the PSU until it's confirmed working for now, this model on the photo is a LiteOn model, it's not the original PSU by LG, it works fine for the 42" PQ3000.

Do all the checks requested at the PSU board, like if 5V is reaching the 5VSTB rectifier, if that big main controller is also being fed 5V.

[tonydix]

Re: Lg 42pq3000 dead

My power board is EAY59544701. I have checked the diode D701 and it is fine.
There appeared to be a short across D304 which I have removed (see photo) the diode is fine but the short remains. Could it be the IC STR W6252 which has legs across this diode ? Thanks
Tony

[Biruslapio]

Re: Lg 42pq3000 dead

Pay close attention to see if it's really a short a not an <1 OHM resistor, or an inductor in parallel with the diode in question.
EAY59544701 is a different PSU than the one in your photo.
I found this repair kit for that EAY model http://www.ohmsupplies.co.uk/PSU-REP...3D-SANKEN1H486 test these components.

[tonydix]

Re: Lg 42pq3000 dead

You are correct. Removed STR W6252 and no short on its pins. Removed resistor and now no short across the diode. So all seems ok. I will now check other components mentioned in the kit, but I am still puzzled by the 5v standby being present until the control board is connected when it disappears. That leads me to think the fault is on the control board or in some startup circuitry. Thanks for your advice. Tony

[Biruslapio]

Re: Lg 42pq3000 dead

You did not inform before that you had 5V stand-by, so if the power supply has 5V on the AUTO_GND pin it should auto-start the relays and turn on PFC and VS/VA voltage.
If it does not something is still faulty with it.

[tonydix]

Re: Lg 42pq3000 dead

So have checked the components mentioned in the test kit. All seem OK.
Power board is on the bench connected to no other boards.
Connect power and we hear the relays click. Measuring pins at pg3 we get :-
m5v 5.1v
va 62v
vs 194v
So does this mean power board is ok and fault lies elsewhere ?
I appreciate your help.
Tony

[Biruslapio]

Re: Lg 42pq3000 dead

Yes, if the stand-by is cutting off with the main board connected, measure the resistance of that rail in said board.

There's more voltages that the power supply produces like 12V and others, but if the main board doesn't even light up it's something with the stand-by.

[tonydix]

Re: Lg 42pq3000 dead

A bare unconnected control board definitely pulls 5v stby to zero when connected to the power board. The unconnected control board shows these resistances to ground :-
17v infinite
12v 1.2k
5v multi 1.4k
5vstby 1.4k
5v mnt infinite
ac detect infinite
relay on 7meg
vavs on 16meg
5v on infinite
5v st infinite
key on infinite

The other voltages supplied by the unconnected power board look ok to me except that 5v on,acdetect and relay on are all 0v

I don't see anything unusual here. Do you ?
Many thanks
Tony

[tonydix]

Re: Lg 42pq3000 dead

Any idea about ic100 on the control board is it 5v or 3.3v and which pin would have the standby supply ?

[Biruslapio]

Re: Lg 42pq3000 dead

Correcting myself, you did inform in post #3 that you have 5VSTB without the main board.

I have a 42PQ30 TV fully functioning, but the main board doesn't have SCART inputs and the layout is different, even so nothing seems wrong with the resistances, this PSU is not being able to handle the 5V STB current the mainboard pulls, there's no other reason for it to cut straight to zero so abruptly.

You can try to simulate the main board by shorting AUTO_GND to GND, 1k resistors from 5VSTB to Relay-on and VA-VS On respectively, maybe before that put a 500mA load on 5V stby with a 10 OHM resistor and see what happens.

[tonydix]

Re: Lg 42pq3000 dead

Good idea I didnt have 10ohms but 13 ohm draws 250 mA with a slight reduction in volts possibly the small dupont cables I was using.
I will try the other tests you suggest.
so is it :-
AUTO_GND to GND
And 5vstby - 1k - relay on
And 5vstby - 1K - VA
And 5vstby - 1k -VS

Many thanks

[Biruslapio]

Re: Lg 42pq3000 dead

yes, you link 5V - 1k to the VA/VS-ON pin at the same connector, not the VS pin.

To confirm you have all the other boards and the panel working you can do the power supply self test, no mainboard, Y-SUS VA/VS/5V plug inserted, the tv should come on with a black screen, and then if you remove the LVDS cable then short the AUTO_GEN pads on the logic board (in the middle of the TV) it will display test pattens.

[tonydix]

Re: Lg 42pq3000 dead

Connected like you suggest get nothing at switch on. Remove all above wait 10 mins and reconnect 5vstby returns and relays click. Short Auto-gnd to gnd relays click and we lose 5vstby. What is connected to Auto-gnd ?
Thanks for your patience.

[Biruslapio]

Re: Lg 42pq3000 dead

AUTO_GND is the power supply's detection of main board, the main board has this pin shorted to ground, so 0V, without it it's supposed to be at 5V.
When there's no main board(AUTO_GND at 5V) the power supply auto-starts as soon as it can when AC is plugged in.

[tonydix]

Re: Lg 42pq3000 dead

So I tried to see what was happening with AUTO_GND.
Power on relays click and 5vstby is 5.1v
Touch voltmeter probe to AUTO_GND. 5.03v still have 5vstby at 5.1v
Now ground AUTO_GND relays click and 5vstby is lost.
Is this expected behavior ?
Thanks

[Biruslapio]

Re: Lg 42pq3000 dead

No, stand-by should always be present, otherwise how would the main board turn on.
Does AC_DET drop to 0V too?
Power supply is faulty in this case, weird because you said you tried two of them.

[tonydix]

Re: Lg 42pq3000 dead

No I do not have a replacement. My only thought now would be to break P1100 connection connect 5vstby to control board and then try to measure current being taken by each supply eg 5v, 12v, 17v to see where shutdown occurs. What do you think ?
Tony