LCD TV With Negative Picture Repaired
This LCD 37″ Samsung TV was brought to me by a neighbor with complaint of white screen with negative picture but there’s audio. First, I opened up the case cover and clean up the dust, see picture below:
I know most often this kind of problem has to do with t-con board,
sso I removed t-con shield and switch on TV and did voltages testing on it, see what i got,: vgh 27.3,vgl -6.03,v3v3:3.35,avdd15.80,vcom6.26, these voltages are within range for 37″ TV I suppose. So went on to test gamma voltages, these are :
(1)15.12 (2)14.92 (3)14.52 (4)7.03 (5)5.53 (6)3.28 (7)2.54 (8)1.74 (9)0.92 (10)0.72 (11)0.59 (12)0.48 (13)0.58 (14)0.47 (15)0.07 (16)0.06 (17)0.04 (18)0.05 (19)0.06 (20)0.22 (21)0.23 (22)0.26.
These voltages supposed to be in descending order but as you can see from no 13 it’s erratic. So I suspected gamma correction ic.
When I touched the IC, it was very hot to finger. See picture below:
Then tested the surrounding components too, which are all ok. So I removed pad on IC and soldered IC out from board. It’s gamma IC number AS15-F. I didn’t get this code type from store, but I got AS15-HG. You can see the old and new IC on the right side of t-con board.
While I was de-soldering the original AS15-f, two gamma pin pads on the board got burnt and removed completely. These are tracks for gamma IC pins no 5 and 28. Well, I still went ahead to solder in the new AS15-HG.
There is no schematic diagram to use to locate were those two tracks connect to, so I try to put tactfulness to play. Since I can still see traces of the tracks from where they cut, I then use analog meter on continuity mode, with one probe place on where track cut and other probe touching components on board.
At the end of it all, I located two separate resistors that are directly connected to broken tracks separately. Then I used thin copper wires to build new tracks from gamma IC pins to the resistors.
At the resistors end, I used soldering method, but at IC end I used 4 minutes glue to adhere copper wires to IC pins, if I had used soldering method, some of IC pins would have shorted together by soldering fluid/lead. It may seem crude way, but it gives me result.
Then I coupled everything together and powered on the TV, the video picture shows beautifully, see picture below of the finished repaired work.
For your information, the customer has been using this TV for 2 weeks now without any problem.
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Note: You can read his previous article on Burnt 85 Watt CFL Bulb Repaired