I recently repaired a 32-inch TCL LCD TV that had no display and no sound. After disassembling the unit, I identified the main board as model 40-A112C1-PWE1XG. During testing, I found that the fuse F1 (3.15A/250V) was blown. Further inspection of the PFC filter capacitor CE1 (450V/150UF) revealed a short in both polarities. Upon closer examination, I discovered that the backlight drive power transistors QW3 and QW4 (both 5N50) were damaged. After replacing these components and the fuse, the TV still didn’t produce any sound, which indicated that the motherboard was functioning properly. This led me to conclude that the issue was with the backlight circuit. I then checked the gate circuit of QW4 and the driver circuit. A thorough inspection revealed that R506 (10Ω) was open, D502 (a 2SK785 composite diode) was shorted, and the backlight oscillator IC OZ9976 (pin 16) was also damaged. Additionally, D511 and D512 (marked S4) were found to be faulty. However, C512 was in good condition. After replacing all the defective components—D502 with two IN4148 diodes, D511 and D512 with IN4148s, R506, and the OZ9976—the TV worked perfectly. The repair was successful, and the TV now functions as expected. Below are some photos of the faulty components and the final result.
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