Source COF Found Short Between VGL & VGH In COOCAA LED TV Model 42S6CG
One of my elder brother’s schoolmate called me introducing himself and informed that there was no display in his TV and sound was ok and this happened suddenly while watching. Though I normally do not make any house visits, this was an exceptional case as he was not fit enough to remove the TV from its wall fix and sought my help. As it was a late evening call, I told him that I would pay a visit the next day morning, being an off for me. I checked the complaint and found that the backlight was on, which I could make out by gently tapping on several places, when the presence could be seen, but the display remained dark. There could be many reasons for such a complaint including panel failure. I understood that the decision maker is his son living in a faraway city and got in touch with him and told him all possibilities and gave a proposal of maximum budget within which it can be set right. I am resorting to this type of approach because of my bitter experiences in a few cases recently, where I brought the TV home, opened it made preliminary tests and informed the customer of the budget, who agreed, but took back the TV next day morning as his son who was abroad wanted his dad to give it to the shop from where the TV was brought. You can imagine my plight!
This happened inspite of the fact that I visited their home to inspect the complaint, helped them fix another working TV as a standby. In yet another similar case, the customer did not inform me about the TV attended by another person before me, with whom he had a rift and took back the TV. In that case, the technician involved had fit a lightning spoiled defective Mother Board purposefully. This customer was very cunning that he kept away this info from me to check to confirm his suspicion. When I offered him the solution and gave the budget, he declined and took back the TV, without never even offering to pay any compensation for the efforts and time spent on his TV. Such are some cunning and ruthless people, though living in my vicinity and known to each other but with no past dealings.
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But for a change, this customer was very straightforward and agreed to my proposals, upon which I dismantled the TV from its stand though I had to really struggle because of the hidden and not easily accessible fixing screw under the holding frame. Though I as well as the Autorikshaw driver tried out our best we could not and the customer’s son helped us by removing the screw from the bottom. The TV was brought home, opened and subjected to thorough cleaning of the inside before moving it to my service table. Let us have a look of the inside:
The preliminary tests include checking the voltage to the panel and the subsidiary voltages such as VGL/VGH/Vcom/AVDD & VCC. The voltage of 12V to the panel was present. But other voltages were absent except the 3.3V. Let us have a look at the ICs used in the scalar board: [IN518, IN603C & IN2812A]
I checked the ohms reading between VGH & VGL and found it to be 44 Ohms, which meant a dead short. In such cases, the first step is to look for any shorted caps on the scalar board. I could not find any strained or shorted cap on it. Then the next step is to cut any one side of the track that goes to the panel. I located a mark on the extreme left of the scalar board, which was easier for me to make an incision. Then the VGL (34.8) and VGH (-6.02) voltages showed correctly:
This surgical test proved that the panel or the COFs (source or side) had a short. The case was then referred to my techiefriend who handled panel bonding and laser treatment, who is located around 30KM away from my home. I took the TV to his shop after getting a date and time convenient. Both he and his son run the shop and he was too good to come and take up my work, even though his son, who handled these types of jobs, had running fever and severe cold and headache. Look at the concern and commitment they have! (He attended only to my case and took rest afterwards!) The VGL/VGH tracks were found burnt and shorted in one of the source COFS, as seen on the monitor of the microscope. (The entry into their working area and permission to take snaps also are special concessions given to me and he never allows anyone else, come what may.)
His son carried out replacement of the COF, which is a time consuming precision job. In this case, he also had to use his laser machine to clean the glass which had black marks on it. New COF bonding cannot be done properly if there are black marks on the area. As though adding salt to the wound, one of the power supply boards of the laser machine had conked off and the sliding motor therefore was not working, which meant manual adjustment! But his son braved all odds and his dad temporarily connected the other supply to run the machine. Look at all special favours done for me, for which I thanked them profusely and prayed God should bless them abundantly.
Anyhow, the net result of all these combined efforts and dedication culminated in a fruitful result as the the TV came back to life with excellent pictures. So, the old adage, which my (late) eldest brother taught me “Sincere and strenuous efforts can never go unrewarded”, became true! I brought back the TV and subjected it for further testing before arranging delivery to the customer’s home and fixing it there in the wall mount stand. Mission accomplished with escalated vigour and enthusiasm, the resultant satisfaction of which had a warm welcome by the collection bag and its inmates!
This article was prepared for you by Parasuraman Subramanian from India. He is 76 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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You may check on his previous article on Surprise Help By Techie Friend For Replacement Of Backlight In ONIDA LED TV Model LE050FNAB2
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