Scaler Board IC CM501 Found Shorted In Toshiba LED TV
Model and Make of the TV : Toshiba 32PU200E1 LED TV
Complaint reported : No picture, but sound ok.
When did it happen: While watching TV
My observation: Complaint genuine.
Action taken: Opened TV, cleaned inside, checked for any bulgy capacitors or other visually traceable component failures. There were none.
Investigations done: Voltages from Power Supply Board were ok. The Voltage at the Scaler Board was checked. Input of 12V was reaching. But the VGL, VGH, AVDD, VDD and VCOM were missing. The voltage to Control IC CM501 at pin 16 and 17 was ok. But this IC was not producing the VDD of 3.3V, which should go to the uController IC to get back the enable voltage to its pin 9. So, this was not functioning. The VGL and VGH tracks were checked offline for any direct short. While the VGH was ok, VGL showed a 97 Ohms short to ground. In order to isolate the section, VGL track that goes to panel was cut. It showed same short.
Conclusion: IC CM501 was defective and should be replaced.
Action taken: Applied liquid solder flux and soldered all the 48 pins together of this 6mm IC. Applied a few more drops of liquid flux. Took a tin sheet, cut a square hole for the CM501 to be exposed, and covered the other areas of the IC to prevent hot air flowing over the tiny components around, and bent the extra length of the sheet on the other side of board for a firm hold. Pressed the tin tightly over the surrounding components, and pressed the inside edges tightly onto the PCB.. Adjusted the temperature to maximum on my SMD Rework Station, and air just to cover this tiny IC. Within seconds, this IC, which had heat zinc underneath, came off.
As a replacement was not available, a booster board was used to obtain VGL, VGH, AVDD and VCOM. Keeping the board outside, applied 12V input and adjusted the voltages thus: VGL: Minus 7.4, VGH: 26V, AVDD: 12V (Though suggestion was to set it to 14, the board did not support higher than 12V), VCOM: 5.6V (for the Gamma IC). Obtained VDD of 3.3V, by tapping from IC No.54328, pin 1 located in the main board.
The wires were soldered to the board and to the respective places marked on the Scaler Board. After rechecking, the TV was switched on, and found to be working well.
So, the board was placed in a slot under the Scaler Board and fixed firmly.
TV was closed and tested for hours together and delivered to customer.
Result : Satisfaction of a different kind, jumped into the bag!
Now let us see the pictures corresponding to the above:
Main Board and Power Supply Board
The defective IC, Scaler Board and the arrangement for removing IC
The Booster Board, its wiring and final placement
My thanks are due to my technician friends, who guide and encourage me in all respects!
This article was prepared for you by Parasuraman Subramanian from India. He is 69 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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