LG 47LD520 Screen flashes 4 times

[eagle00799]

Hello Everyone, I am trying to repair a LG 47LD520 LCD TV and the problem is when powered on the red led turns blue and the sound comes on and stays on but the backlights come on for maybe 2 seconds then off then back on then off, back on then off, back on then off and then the tv powers off. So the tv screen flashes a total of 4 times before the tv powers off. Voltages seem to be right with the exception of the ERROR voltage goes to 3.4v when lights go off and back to 0 when they are on. Any suggestions? Hate to spend the money on a board if it's the backlights themselves.

[vinceroger69]

Re: LG 47LD520 Screen flashes 4 times

this looks like a ccfl tv so may have the 2 seconds to black fault this is usually caused by the inverter boards or a bad ccfl tube/wiring on the left and right side of the set are there boards under the metal covers?

[dick_barton]

Re: LG 47LD520 Screen flashes 4 times

Check the solder joints on the transformers. It may be best to resolder all the joints. Inspect the state of the two blue capacitors at the connectors to the tubes
Can you measure the resistance of the transformer, primary and secondary and compare them to each other. They should read the same.

Also check the wires from the connectors to the CCFL tubes into the panel since there have been problems with the insulation being damaged and sparking to the chassis causing the fault.

[eagle00799]

Re: LG 47LD520 Screen flashes 4 times

The inverters are integrated with the power supply and there are no metal covers. The t-cons must be the type that are permanently bonded to the panel, I will check the transformers and solder joints next.

[vinceroger69]

Re: LG 47LD520 Screen flashes 4 times

The inverters are integrated with the power supply and there are no metal covers. The t-cons must be the type that are permanently bonded to the panel, I will check the transformers and solder joints next.

sorry was hard to tell in the first picture as where the wires go to on the sides of the panel it looked like there was removable covers and didnt know if there was pcbs that maybe at fault there too. but do the tests dick suggests and see how you get on

[eagle00799]

Re: LG 47LD520 Screen flashes 4 times

The transformers measure close to each other at 14.6 and 14.9 ohms, the blue caps next to the transformers measure 1.79 and 1.76 ohms. No signs of bad solder joints.

[eagle00799]

Re: LG 47LD520 Screen flashes 4 times

The blue caps that Dick Barton is referring to are the ones inside the panel on the boards the tubs connect to?

[vinceroger69]

Re: LG 47LD520 Screen flashes 4 times

i think he means the ones on the psu by the transformers the ones you have tested im not sure what parts are on the pcbs on the tube ends.

[eagle00799]

Re: LG 47LD520 Screen flashes 4 times

I think I found the problem!

[vinceroger69]

Re: LG 47LD520 Screen flashes 4 times

yes ive saw that fault before on that type of tube/fitting not sure if you can possible stripdown and clean or replace that pcb if you can get one i think threr eefl type tubes too.

[eagle00799]

Re: LG 47LD520 Screen flashes 4 times

Yep, not sure if its worth fixing a 2010 lcd tv. Better off buying a new one but i'll look into parts cost and see what they would like to do. Thanks for your input, you guys are a huge help here.

[vinceroger69]

Re: LG 47LD520 Screen flashes 4 times

i personally would look for another pcb for it as its been arcing across the pcb you may have issues cleaning it properly then you have the tube holder socket not sure if thats repairable the main issues is removing the tubes there so fragile i hate doing them big risk of breaking them.

[eagle00799]

Re: LG 47LD520 Screen flashes 4 times

Been there done that, the plastic holders that hold the tubes are so brittle they break period. And that bulb looks dark though out so its probably shot.

[vinceroger69]

Re: LG 47LD520 Screen flashes 4 times

hard too say what to do the as by the time you have sourced a new tube plus the pcb then you have to fix the plastic tube holder/supports (maybe some silicone will do the job ?) pity you cant find a identical cracked screen set and make one out of the two.