Troubleshooting "No Signal" Symptom In Hisense TLM55V88GP LCD TV

Symptom: VGA Input “NO SIGNAL”

When testing this LCD TV, all other input were found to be good except the VGA input. When plug in the VGA connector to this LCD TV from desktop computer or even laptop the result were the same- “NO SIGNAL” error message shown on the screen.

This LCD TV was used in the shopping mall for displaying content purpose.  Since it is a display set in a shopping mall, the customers and the staff always plug and unplug the VGA connector without turning the power off causing the above error to appear. Others input of this LCD TV was not affected except the VGA input. 

The troubleshooting will be on the VGA input circuit and below is the VGA input signal diagram 

R, G and B lines open circuit will not cause the above symptom except if there is component shorted. If the HS or VS line (VGA connector pin 13 & 14) have an open circuit the above symptom will appear because no signal from the CPU could pass through.  In this LCD TV, I found a resistor (R103-100ohm) that is located in series with the HS line had an open circuit. The problem now was that the error message did not go away even the SMD resistor (R103) was replaced.

I continued to check on the components that is corresponding to the R, G and B line (pin 1, 2 and 3 of the VGA connector) and found Z7, Z8 and Z9 were shorted. Those SMD resistors R98, R99 & R100 (all 75 ohm) that is connected from the R,G and B line to ground were open circuit too.

Components located in the pin 11, 12, 15 (VGA-SDA, DDC-SDA & DDC-SCL) were found to be good. This LCD TV was brought back to life again after the components were replaced.

Below is the picture where the defective components were located.

Conclusion-Hope you have enjoyed the article and remember to check all components in any input if you found that the particular input is not working be it a VGA input, HDMI and etc.

The above article was contributed by Kent Liew

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