LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

[MisterD]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

LG using black coated screws to mount power supply board to chassis, maybe poor ground connections, see top side of PS board four corners have flat chrome metal tabs, I'm not sure but I think the top side of the board is grounded by the screws tightened down and giving top side grounds through the screws being threaded into the chassis, the bottom side of the board has solder at mounting holes for grounds once all screws are tightened down
I would think the screws would not be black coated but be chrome instead.I have seen this cause what you are having with backlight flashing and tv shutting down.

[U2vipergirl]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

I also have this issue on a 42l7d-ub. Originally this unit would not turn on so we replaced the caps that were reading as bad. Now it turns on and the back light comes on as does the channel in the corner and the sound but then the back lights go on and off 3 times and it shuts down. We know this is a board issue because we had another LC7d TV that just had bad caps and we fixed that board got it working put it in this unit and it fired right up. Still looking for answers

[dskall]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

You replaced the caps per this post?

[U2vipergirl]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

we replaced the 11 caps marked in red in this image and tested the rest and they test as good.

https://drive.google.com/file/d/0B33...R3X0FXbTQ/view

[dick_barton]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

Check the two blue capacitors by the connectors to the CCFL lamps and it may be worth re-soldering all the joints on the HV transformer alongside them.

You may be unfortunate and it could be a poor connection on one of the CCFL tubes or even a failing tube.

[U2vipergirl]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

It's not a tube because I tested this TV with another board from the same model # and it worked fine so I know its something on this board. Just not sure what. We tested the 22k 6v Ballast caps (blue) By the connectors to the CCFL lamps. They seemed good. This morning we re did the joints on the HV Transformer. Just in case cause someone on another board about this issue with tv's said that was his issue. Really lost now as where to go next.

[dskall]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

The caps you replaced are for secondary voltages. The ones dick barton point out could cause a problem. That is power supply for ccfl's. "They seemed good" maybe worth changing.

[U2vipergirl]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

OK gonna buy the Ballast Caps near the connectors for the ccfl lamps. I Should be posting within the next week letting people know if that solves it or not. I hate when so many people ask questions and then someone solves it but they don't post back to whether or not it worked.

[dskall]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

Nice to know if advice fixed problem. So we can more easily help others

[U2vipergirl]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

Well it was not the Ballast (blue) caps on the inverter side of the board. . I guess the only thing left to do is buy another board since I know this is a Power board issue since switching out the board from another tv worked. Unless you have any other Ideas on this?

[budm]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

What is the PFC Boost dc Voltage on the main two filter caps in the hot side?

[U2vipergirl]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

I think you got a bit ahead of us lol. I am not quite sure which two caps you are talking about

Here is the schematic for the board:
https://drive.google.com/file/d/0B33...BieXpEX0k/view

Can you please tell me the # on the schematic next to the caps you want me to test?

[budm]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

C607 or 608.
You must be real careful since you are working on the hot deadly side of the circuit, you should at least plug the unit into GFCI outlet.
It will be good to upload good clear straight shot pictures of the top and the bottom side of this power supply-inverter board.

[U2vipergirl]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

I couldn't find a video on how to do this and since we have always tested lower caps out of circuit we wouldn't know where to begin with that. We are not quite to that level of board repair yet. but were smart enough to know not to do it unless we know exactly how lol. My brother thinks it might be one of the transformers that could be bad because before we replaced all the regular caps it was chirping. T101 on the schematic But we've never tested one of those either. If you have any reference videos or webpages on how to test either it would be greatly appreciated. We want to learn to do it the right way safely.