VGH Voltages Showed Negative In SONY LCD TV MODEL 32EX310 With Line/Bar On Screen
This TV was brought to me by a regular customer, picked up from his relative’s house, with a complaint that only lines are seen on the screen, though audio is there. I opened the TV and after thorough cleaning brought it to my service table for investigation. Knowing that all functions are working well, I straightaway turned my attention to the T-con Board and checked all the voltages.
Since this had two COFs going to the panel from the T-con Board, I removed one and switched on and did the same on the other two and removed both COFs and checked. Following was the result:
As you can see, the VGH was showing a negative voltage of 2.15 instead of around 24 to 28V. The booster IC No. TPS65170 was not producing the VGH pulse, though the tappings from the power supply was coming. Noticed one diode burnt and open in the circuit. I replaced both the schottky diodes by two removed from a scaler board sent to me earlier for using a scaler IC. Since the size was bigger, I had to mount it very oddly, just serving the purpose.
I checked all other components in the VGH section and did not find any defects. After checking with my techie friends, the next step was to remove R716 that carries the VGH to panel and connect a 24V booster board directly to the panel, taking the 12V from the LVDS connector on the T-Con Board.
They also advised me to check for any short between VGH and ground and VGH & VGL. I did not find any. I adjusted the booster board to give out 24V from the 12V.
Then wired inputs and outputs to the T-con board, after removing the R716 resistor. Opted to give only 24V instead of 26 or 28, as the booster board is of high current capacity. The display was back on the screen and it was pretty good to see it.
So, housed the board well under the main PCB and fixed it using tape:
Tested the TV for several hours and it worked flawlessly. After having satisfied on its performance, fixed the back cover and connected it to a cable network and again tested it for more than 10 hours. The only problem that I could see, which is common when we do such bypass work, is a few unstable lines appearing on the screen but these go off on its own within a few seconds.
Once the TV comes out of this cold start problem, it would work continuously without any hitch. So, mission accomplished with a lot of satisfaction getting added to the collection bag.
This article was prepared for you by Parasuraman Subramanian from India. He is 72 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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