LG 47LC7DF sound 2 second backlight

[Bobabouey]

Hello,
I have a LG LCD 47LC7DF that has sound and will flash the backlight on for 2 seconds (then goes black), on power up. I re-capped all the secondary PSU caps (None bloating or leaking), but the problem remained the same. Now, if I unplug the 'C' slave inverter board (4 total A,B,C,D), from the PSU, the backlight comes on, and i have a picture, albeit a little dark in the 'C' inverter corner. I then replaced the 'C' 'D' (pair) inverters assuming 'C' had gone bad. Well, that's what 'assuming' gets me, because it still does that exact same thing, (sound, 2 second backlight flash). And again, when the 'C' inverter is unplugged from the PSU, I get the other three inverters to light up? All 4 inverter PSU connectors have 24 volts, and the controller PSU voltages are within specs of what's printed on the board (the ones that actually have voltage values). I apologize, and would appreciate leniency for not being more technical with my observations (first attempt for this type of repair). Any, help at all would be greatly appreciated. Thanks!

[Bobabouey]

Re: LG 47LC7DF sound 2 second backlight

Here's how it looks with 3 out of the 4 inverter boards working (inverter board 'C' is disconnected from the power suppy).

[PlainBill]

Re: LG 47LC7DF sound 2 second backlight

Here's how it looks with 3 out of the 4 inverter boards working (inverter board 'C' is disconnected from the power suppy).

This makes me wonder is there isn't a problem with one of the CCFLs connected to inverter board 'C'.

PlainBill

[Bobabouey]

Re: LG 47LC7DF sound 2 second backlight

Hey Bill,

I even went so far as to disconnect all of the CCFLs from that inverter board, but it still did the 2 second flash of the other A,B,D, inverters CCFLs. It's only when that inverter board 'C' is disconnected from the PSU that I get the 3/4 backlight picture as seen?

[PlainBill]

Re: LG 47LC7DF sound 2 second backlight

Hey Bill,

I even went so far as to disconnect all of the CCFLs from that inverter board, but it still did the 2 second flash of the other A,B,D, inverters CCFLs. It's only when that inverter board 'C' is disconnected from the PSU that I get the 3/4 backlight picture as seen?

Of course. All but the very cheapest inverters have a controller which detects various faults and will shut down if a fault occurs. Possible faults include a CCFL which draws too much current, and a CCFL which does not draw enough current. Obviously, a CCFL that was disconnected (or broken, or had a broken wire) won't draw enough current.

Depending on the design of a multiple inverter system, it is entirely possible that removing power from an inverter would NOT cause a fault. You must substitute a CCFL with similar characteristics for each CCFL in turn on the suspect inverter.

PlainBill

[Th3_uN1Qu3]

Re: LG 47LC7DF sound 2 second backlight

Try swapping the inverter boards around if you can.

[Bobabouey]

Re: LG 47LC7DF sound 2 second backlight

Thanks Bill,

I never considered a disconnected CCFL would cause a shut down vault (no voltage as opposed to an over voltage). I appreciate the direction, and will substitute in know good CCFLs to see if that is indeed the problem.

[Bobabouey]

Re: LG 47LC7DF sound 2 second backlight

LG 47LC7DF sound 2 second backlight: CCFL Removal?

I'm hopping someone can give me a tip or two for removing (how to get to them)? Does everything need to be removed off the back panel, as well as the back panel itself to gain access to an individual CCFL? I see an unusual type of fastener (Picture #2)? Not sure how it get's removed? Maybe it doesn't? Any tips, tricks, or proper steps, would be greatly appreciated. Thanks!