Power Cycling issues with LG 52LB9DF-UA AUSLLJM

[Pioneerx01]

I am having problems diagnosing this LG TV. When I got it almost every capacitors on PSU was bad, so I have replaced them. I have also replaced caps on the separate master and slave inverters.

The TV power cycles. When I plug it in, TV fully comes on, back-light, screen and sound. It remains on for a second or so and shuts down (relay clicks out). Then it turns on again and process repeats.

The 5V stand by voltage remains constant at all times. The pwr_on pin toggles between 3V and 0V as the TV turns on and off.

I have disconnected the main board and manually jumped (with resistor) the 5V stand by with power on pin and the power supply turns on and remains on. Then I also jumped the back-light control pin and they too remain on. If my logic is sound, the power supply, inverters and CCLFs appear to be OK. That leaved the main board and subsequent boards.

Any thoughts what should I look at?
Thanks

[ReeceyBurger123]

Re: Power Cycling issues with LG 52LB9DF-UA AUSLLJM

Heat mainboard with a hairdryer see if it makes any difference, normally the Smd caps on these fail.

[Pioneerx01]

Re: Power Cycling issues with LG 52LB9DF-UA AUSLLJM

Hey, that's a neat test. It worked. The TV turned on and stayed on for at least a minute, then I turned it off. Then it went back to power cycling when I turned it back on again.

Anyways, that seems to point to bad main board. Is there any "easy" way of determining with of the SMD caps went bad? Or should I replace the bigger ones and see?

Thanks for this tip. It is definitely a keeper.

[ReeceyBurger123]

Re: Power Cycling issues with LG 52LB9DF-UA AUSLLJM

Nice, normally no easy way of finding the bad ones unless you have an esr meter. Or you could put a card tube over the hair drier to direct the heat to certain areas giving you a better idea of which area/caps are at fault.

[ReeceyBurger123]

Re: Power Cycling issues with LG 52LB9DF-UA AUSLLJM

Also try heating the main heatsink up as I know Lg mainboards have issues with failing BGA solder.

[Pioneerx01]

Re: Power Cycling issues with LG 52LB9DF-UA AUSLLJM

Sadly I do not have ESR meter. I was thinking of baking the board in oven as a last resort. I fixed one LG TV like that, but totally different symptoms. Replacement board is only $50, so I just might do that if nothing works. Thanks for your input.

[ReeceyBurger123]

Re: Power Cycling issues with LG 52LB9DF-UA AUSLLJM

No worries keep us updated on what you do