Hisense LCD TV logic board troubleshooting example - appliance repair - Database & Sql Blog Articles

Hisense LCD TV Logic Board Troubleshooting Example

Symptom: The TV powers on normally, the backlight works, and there is sound, but the screen remains black with no image.

Fault Analysis: Since the TV boots up, has a working backlight, and produces sound, the issue is likely limited to the display cable, the logic board, or the screen itself. To narrow it down, further testing is required.

Disassembly and Inspection: After checking the power supply voltage (12V) on the logic board, everything seemed normal. Then, I disconnected the display cable and powered on the TV again. Interestingly, the screen turned white for a moment before going back to black. This indicated that the screen was still receiving power but not displaying any signal. Using a multimeter, I checked the resistance of the power supply section and found it open, which suggested a blown fuse or a failed power protection component. Tracing the circuit, I discovered a surface-mount fuse (SMD fuse) that had opened.

As shown in the image below, this small SMD fuse is located near an inductor in the upper right corner of the board.


The marking on the fuse reads "UD." I'm not sure what its rated current is. If anyone knows, please let me know. It's frustrating that such critical information isn't easily accessible.


A common cause of such a failure could be a shorted filter capacitor. These components are known to fail frequently. Upon closer inspection, I noticed a yellowed capacitor near the bottom right of the board (labeled CP2). It appeared to have been overheated and was clearly shorted. I removed it and confirmed the short with a multimeter.

Here's the faulty capacitor:


Next, I checked the 12V power supply section for any shorts and found none. Since the SMD filter capacitors were already damaged, I decided to replace them with new ones. However, since I wasn’t certain about the rating of the SMD fuse marked "UD," I opted to temporarily replace it with a 0-ohm resistor to test the system.

The repair result was successful. After reassembling the board and powering on the TV, the screen returned to normal operation.


Conclusion: This repair highlights the importance of checking both the power supply and filtering components when dealing with black screen issues. Sometimes, the smallest parts can cause major problems. If you're facing similar issues, start by checking the power supply, capacitors, and fuses first.

PS: If anyone has information about the rated current of an SMD fuse marked "UD," I’d really appreciate your help. This kind of detail is often missing from technical documentation.