LG 50PQ6000 unstable 5v standby

[tom66]

Re: LG 50PQ6000 unstable 5v standby

Both are incorrect... It should be 5V by any means...

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

Agreed! Guess its a good start.

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

Im gonne jump back to page 4 later today and do a couple of the tests I went through before.

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

Ok had a little time to have a play with this again today:

Stand by 5v board unplugged 4.43VDC

Voltage on J22-GND = 12.8v DC

Voltage across the 2 BIG cappasitors 400v then drops until the relays click again.

The relays click every 10 seconds on/off.

Looks like something is been sensed not right and not letting it power up. I think its a different problem to before.

Standby voltage definately looks low.

[tom66]

Re: LG 50PQ6000 unstable 5v standby

Does look odd, any adjustment for it? Also, how is it with main board connected? Is there an AC-DET pin, if so, what does it measure?

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

ok cant see if there is a 5v adjustment anywhere just a VA and VS adjustment.

AC detect is only a few mV with the board dissconnected but spikes as the relays click. The spike is a bit hard to measure on a DVM its so quick.

With the board back in the TV there is no AC DET until you hit the power button the red stand by light comes on relays click and the red standby light goes off and stays off. With the TV power button pressed in the AC DET pin is 4.42VDC

After one attempt to start the TV shuts down with no red stand by LED on at all.

No components are getting hot that I can feel.

Standby voltage stays at 4.31.

[tom66]

Re: LG 50PQ6000 unstable 5v standby

Do you see a KA431 or KIA431 or TL431 on the board anywhere.

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

KIA 431A 941? I have found 4 on the power board.

[tom66]

Re: LG 50PQ6000 unstable 5v standby

Yes, the nearest one to the standby section, the voltage between pin 2 and 3, it should be about 2.5V.

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

In the moment the relay clicks IC102 a KIA 413A jumps upto 9v then drifts down to 0.4v.

[tom66]

Re: LG 50PQ6000 unstable 5v standby

I made an error it should be between 1 and 3 I think.

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

ok will try again. :0)

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

In the moment the relay clicks PINS 1&3 IC102 a KIA 413A jumps upto 6v then drifts down to 0.6v.

[tom66]

Re: LG 50PQ6000 unstable 5v standby

Final try, what does pin 1-2 measure?

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

IC102 pins 1 and 2 = 1v then jumps to 2.28v momanterily on relays click.

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

There is an inductor thats making a noise L102 and when you hear the 2 relays click you can hear other parts of the TV start to fire momanterily.

[tom66]

Re: LG 50PQ6000 unstable 5v standby

2.28V should be 2.495V, error is = 8.61%.
4.43V should be 5V, error is = 11.4%

It's close enough to call that it could be the issue. But I'm not sure how to rule it in or out. You'd have to test it out of circuit to be certain.

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

ok cool I can get it out of circuit. Just how do I test it?

[tom66]

Re: LG 50PQ6000 unstable 5v standby

Datasheet has diagram
page 20, first schematic.
https://cdn.badcaps-static.com/pdfs/...8a1d8057ef.pdf

Or just replace it, if you have an old computer psu it's bound to have one of these.

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

Just looking at some utube vids. like a diode test?