Common for resonant capacitor C6 breakdown (short circuit) or low voltage (soft breakdown), should be replaced with the same capacity of high quality polyester or CBB capacitor with the voltage above 1kV. Open tube filament. If LED lamp tube is not seriously blackened, it can be used in emergency after connecting 0.047μF/400V polyester capacitor at both ends of the broken wire lamp pin. R1 and R2 are open or variable (generally, R1 is more likely to fail) and replaced with 1/4W high quality resistance of the same resistance value. The LED lights flickered. If the LED lamp tube is not seriously black, check whether D5 and D6 have false welding or open circuit, if D5 and D6 soft breakdown or filter capacitor C1 leakage and bad, will also make the light flicker.