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Old 11-17-2012, 03:23 PM   #1
picklesman
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Default LG 42LG30-UA - On for 2 seconds then black. Burnt connector to inverter

Hello there.

The TV will turn on for about 2 seconds and then go to black. After opening it, I noticed that the connector on the power supply board is burnt, as if too much current was being drawn. I've attached a photo of this.

I took some measurements on the inverter board closest to the power supply (master?), as mentioned in this thread:
http://www.badcaps.net/forum/showthread.php?t=20203

The backlight seems ok when it's on for the 2 seconds, so I didn't check the bulbs.

Does it look like I should just order a replacement master inverter? What else can I measure to narrow down the issue?

thanks.
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File Type: jpg lcd1.JPG (897.5 KB, 28 views)
File Type: jpg lcd2.jpg (846.8 KB, 30 views)
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Old 11-17-2012, 04:50 PM   #2
tom66
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Default Re: LG 42LG30-UA - On for 2 seconds then black. Burnt connector to inverter

It is actually quite a common fault for the inverter connector to get burnt. What typically happens is the connector isn't clipped in properly at the factory or the TV gets bumped and the connector moves; it then doesn't make proper contact and has high resistance, so it gets very hot. What you should do is measure the 24V on the inverters for those two seconds when it's not working. If it drops below about 22V, you need to either replace that connector or solder wires from the inverter to the PSU. (You could use some screw connection blocks to make future service easier.)
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Old 11-17-2012, 08:12 PM   #3
picklesman
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Default Re: LG 42LG30-UA - On for 2 seconds then black. Burnt connector to inverter

Thanks so much for the reply. That makes sense and could very well be what happened here. I'm not sure if it's visible from the picture, but some of the wires are the burnt ends are down to a couple of strands.

I'm going to solder a much thicker wire from underneath the connector on the power side to the inverter board and fire it up. If it still doesn't work, then I'll see what else it could be.
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Old 11-17-2012, 09:18 PM   #4
picklesman
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Default Re: LG 42LG30-UA - On for 2 seconds then black. Burnt connector to inverter

OK, so I soldered on a thick wire connecting the two boards and the problem persists. I measured 24.56 V on the inverter board where the power comes in, so that doesn't seem to be the problem. Any other ideas of what I can measure?

I've attached a pic showing the black cable I soldered.
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Old 11-17-2012, 11:28 PM   #5
retiredcaps
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Default Re: LG 42LG30-UA - On for 2 seconds then black. Burnt connector to inverter

This was originally written for computer LCDs, but it applies to LCD TVs as well.

2 seconds to black can be

a) bad caps
b) bad ccfls
c) bad ccfl wiring (especially the return wiring)
d) bad secondary windings on the inverter transformer

More details starting with post #19 at

http://www.badcaps.net/forum/showthread.php?t=10419

Also, see budm's Inverter tester using old CFL

http://www.badcaps.net/forum/showthread.php?t=19987

PS. One retiredcaps' bonus point for a picture of your Fluke 17B.
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Old 11-18-2012, 03:14 AM   #6
selldoor
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Default Re: LG 42LG30-UA - On for 2 seconds then black. Burnt connector to inverter

If as in your pic you are indicating the secondaries on the transformers are open then
you will need to replace them or get a new board. Unless you know those are the secondaries check by checking all the pins 1-2 1-3 1-4 1-5 2-3 2- 4 2-5 3-4 3-5 3-6and so on, on both transformers secondaries should be the highest ohms and should be similar on both transformers.
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