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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Parasuraman S
December 22, 2021 at 9:33 pm
I have a similar problem with a Sony TV. Unfortunately, we do not get original ICs in the market. I replaced the IC once, but it did not solve the problem. So removed it and I am yet to try with another.
It is a strange coincidence that same IC number is the culprit always! Many thanks for sharing! It was very useful!
Albert van Bemmelen
December 22, 2021 at 9:33 pm
Good job Imoudu! But I at least easily would have soldered those 2 wires onto the replacement smd pins of the AS15-HG chip with solder. I wonder how those still make contact now with only 4 minute glue if you didn't use some sort of silver glue.
Eric Rice
December 22, 2021 at 11:49 pm
A very very thin pointed tip for your soldering iron with some magnification to look thru will help. Practice on junk boards before doing final work. You’ll be a pro at it in no time!
Blessings my friend,
Eric
William Shaw
December 23, 2021 at 1:24 am
Remarkably creative job. Congratuations! Good insight for me on the T-CON board. I'll keep that in mind.
Thank you.
Waleed Rishmawi
December 23, 2021 at 3:00 pm
this IC is called the gamma IC which have to do with colors and the display on that panel. I have a done a repair like that before and worked just fine. my only issue to find good IC's on line. last time I bought about 50 of them and I had a about 20 of them defective sad to say. thanks for sharing and have a blessed day
Mark
December 23, 2021 at 4:44 pm
Great job Imoudu!
It does take practice to solder those tiny little ICs. I is easy to remove any bridging of solder, simply by dragging the iron along the pins. Using solder is the best way to ensure you have a permanent contact.
Well done!
Imoudu Onwumah
December 23, 2021 at 5:46 pm
Mr Parasuraman.S,Albert.V,Eric.R,William.S,Waleed.R,Mark.
Thank you all for your comments sirs. I was told by a friend there are fake ones of AS15 series of this ic.When I used glue,I did check it up with the use of analog metre for continuity.I am doing this kind of repair for the first time,as Eric suggested I will have to practice with junk boards:"practice makes perfect" it's said.Thanks Mark,your suggestion is noted.
Waleed Rishmawi
December 27, 2021 at 4:57 pm
Imoudu: keep up the good work you are doing fine. yes practice makes perfect and most of all to have the love to do repair work otherwise you are wasting your time. have a blessed day
Yogesh Panchal
January 2, 2022 at 4:02 pm
Imoudu,
Good attempt for fixing.....always use good quality solder flux & refresh the old solder first before removing the IC.