How to troubleshoot V315B3 T’Con board. For 32LB30 – LE32A336 – LE32A4361DXXC – LN32A450 LCD TV
V315B3-C04-T-CON-BOARD: FROM-32LB30QC, LE32A336, LE32A436T1DXXC,
LCD-LN32A450C1D
a. TV No Display but Sound Ok and the backlight working.
Check the T-con board and found that SMD fuse burnt. If this type of symptom doesn’t just put another fuse to power on the TV, it may damage seriously again.
> Since the SMD fuse burnt, must using the Multimeter checking Vcc input line with GND ohm values. The values show it is normal, continue checking the other voltages lines like VGL, VGH, VDA & etc. Finally found VDA line to GND was shorted and it was 0 ohm. Disconnect the both FPC cables, VDA line still remain shorted. Now checking their VDA line corresponding components and found the CP12 shorted. After remove CP12, VDA line ohm values back to normal and testing this CP12 was confirm it had shorted. After replace SMD fuse and CP12, the VDA output 15.9V and TV is working properly.
b. No Display but Sound Ok and the backlight is working
> Check the Vin have 12V input and other voltages lines also normal except VDA line is 0V. Because of the T-con board DC-DC voltage control by the timing control, as follows: VDD25, VDD18 => VDA => VGL =>VGH, the VDA is control by TPS65161 pin 27 output logic high/low signal (voltage) to QP1 (P-ch MOSFET) pin 4, when signal logic low received the MOSFET is switch ON and the VDA voltage has output and reaching to the GAMMA correction IC.
Test the QP1 MOSFET, pins 1, 2 & 3 have 15.9V. It had proved that the VDA voltage is present. Testing MOSFET pin 4 is logic low signal, but pins 5, 6, 7 & 8 no VDA output Remove and testing the QP1 MOSFET and found it had opened circuit. After replace QP1, the VDA got 15.9V output and display back to normal.
Note: If don’t have the QP1 on hand, temporary can just using a wire connect QP1 pins 1 and 8, so it will bypass the QP1 switch function and testing T-con board is ok or not.
c. Screen Shows Vertical Color Stripes. The stripes are slowly to increase.
> The vertical color stripes is slowly increase till full screen of vertical color stripes. This symptom could be the VGH circuit abnormal. Check the VGHP has 21V but VGH is 0.3V only instead of 21V. Testing QP7 (2N7002) pin 2 is logic high, pin 6 has 21V. For testing purpose, try to using a wire connect QP7 pin 6 to pin 4. After connected the wire, the VGH has 21V output now and display show perfectly. After replace the QP7, display is working properly now.
d) Screen Fully of Vertical Stripes and Sometime NO Display
> From the above symptom, it could be one of the DC-DC circuits abnormal and causing this problem. Check the DC-DC circuits and found that VGH voltage not stable and it is about 4.6V only. After some time, the DC-DC circuits all voltages will no output (No Display) and need to power off and then on it again the voltages will come. When the no voltages output, power off the TV, using the finger touch the IC and feeling their temperature is a bit high but not extremely hot. Suspect the FPC cables problem; remove both CN1 & 2 and measure the VGH voltage still not stable. So the problem is still in VGH circuit line. Check the VGH line corresponding components, by disconnecting the CP19, CP43 and found that when removed CP43, the VGH voltage line is back to 21V! Replace CP43 with 1uF/50V, the T-con problem solved