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LG 47LC7DF - Low voltage issues    
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Jferris84



Joined: 16 Apr 2017
Posts: 4
Location: WI

PostPosted: Sun Apr 16, 2017 9:15 am    Post subject: LG 47LC7DF - Low voltage issues Reply with quote

LG LCD 47" 47LC7DF with voltage issues. It turn on but no picture and the back light works. I measure the voltage from the power supply to the main board. All the voltage are good but one. The pin that label 3.4V ON is only getting 2.38V. Is this to low? I also checked the voltage from the main board to the Tcon and its getting a voltage that jumps around from 12.08 to 12.18V. The voltage from the Tcon to the LCD panel is between 1.04V to 1.30V with no voltage dropping or 0V. Does anyone know what can cause this? Thank you.
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JTS1957



Joined: 21 Jan 2009
Posts: 2305
Location: Far, Far Away

PostPosted: Sun Apr 16, 2017 9:52 am    Post subject: Reply with quote

C202, C206, C217, C221
Jferris84



Joined: 16 Apr 2017
Posts: 4
Location: WI

PostPosted: Sun Apr 16, 2017 1:31 pm    Post subject: Reply with quote

Thank You
Jferris84



Joined: 16 Apr 2017
Posts: 4
Location: WI

PostPosted: Wed Apr 19, 2017 2:56 pm    Post subject: Reply with quote

Any other ideals? I replace the four capacitor with new ones and still only getting 2.38V on pin 3.4V ON.

Thanks
kuhurdler



Joined: 28 Dec 2006
Posts: 2852
Location: Overland Park, KS

PostPosted: Thu Apr 20, 2017 7:55 am    Post subject: Reply with quote

Check the voltage regulators on the mainboard. I think that 3.4V On signal is supposed to be from the main TO the power supply.
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JTS1957



Joined: 21 Jan 2009
Posts: 2305
Location: Far, Far Away

PostPosted: Thu Apr 20, 2017 11:49 am    Post subject: Reply with quote

IF you have a external variable power supply available you could input 3.4V and see if set will work. At least then you would confirm you're on the right track.
Jferris84



Joined: 16 Apr 2017
Posts: 4
Location: WI

PostPosted: Thu Apr 20, 2017 1:43 pm    Post subject: Reply with quote

I cut the wire from the main broad to the power supply. With the wire not connected to the power supply the main broad is putting out 3.264V, which is enough to tell the power supply to turn on the back lights.

Now I am thinking there is a problem with the main board voltage to Tcon because it still jumping around. I'm new to this but the voltage to the Tcon should be steady right?
kuhurdler



Joined: 28 Dec 2006
Posts: 2852
Location: Overland Park, KS

PostPosted: Fri Apr 21, 2017 7:08 am    Post subject: Reply with quote

yes, the power wire to The Tcon should be steady.
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