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LG 42LB585V - Backlight issue.

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Turnip:
Hi folks,

Got one in with a quick flash of 'LG' but sound continuing. Leds fed by two wires so all in series.

Test measurements were a bit odd. Voltage initially 250v dropping to 105v but noticed on the meter there was a reverse resistance I hadn't noticed with earlier LG Led sets.

Took the screen apart finding 4 strings of 8 Leds that required 40v to light up per string. About to replace O/C Led from stock but noticed the new Leds were a little bigger and needed 5.5v to fire up.

To Ebay where China supplies 6v LG Leds at £5 for 50 - Wish I'd got some as UK ones are a pound a pop at the moment.  Nice side is that Leds can be replaced by snipping off the old one, cleaning up the PCB strip and fitting the new one with LMP solder. Taking out the plastic reflector sheet would be a real fag as there are dozens of securing plastic devices that don't seem to come off so easily - Chris.

downunder:

Hi Chris,

8 LEDs needing 40 volts to fire should have rung alarm bells. Not knocking you, mind, cos we tend to forget there are 6V LEDs in use. But keep up
the instructive banter. I guess it's like here in the UK - once we old fogies have gone to the other side, there will be none left to do the service.
The DIYers will inherit the void.             Bruce

bonesy:
Hi Chris,my only advise with the LG LED's,check & make sure all your strings are evenly lit,if any are just slightly dimmer,good chance within a short space of time it could bounce back to bite you,cos another string has failed.Has happened to me twice now,so any looking slightly dimmer get replaced now.Lg seem to be very poor LED wise.

Turnip:
Hi Bruce

Thanks, this LG was my first with 6v Leds, so was naturally confused but glad I didn't slip in a 3v one and wrap it up.

Out of interest, what's with 6v Leds that seem to have a diode conducting with reverse voltage and are capable of 3 watt dissipation - For a while ?

Thought try find a service manual to see if the supply is unusual, though it appears DC as per usual. Naturally Now't available.

Thanks bonesy. In this case they all look much the same, and my duff one was burned out, maybe due to an initial bad soldering issue - Chris.

sinclairtv:
Dont the plastic securing bits just slide out?

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