Hisense LCD TV LED42K11P irregular shutdown maintenance examples - appliance repair - Huaqiang electronic network

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A Hisense LCD TV LED42K11P user said that it does not stop for more than 2 hours during the viewing. After the shutdown, it can't be turned on immediately. It can wait for a while to start watching again. After picking up the machine, the boot shell is shut down and the 5V waiting machine is measured. Voltage and green light are always on. The other voltages are measured to be zero, but at this time, the motherboard start command STB is still 2.35V. I think the motherboard does not issue a shutdown command is the power supply itself, the machine is a two-in-one power board RSAG7.820.2264/ROH. First measure the PFC voltage is only 320V! In this case, it may be that the PFC circuit is not working or is too low, causing the main power to stop. Follow the circuit to check the PFC chip NCP33262 pin 8 and the main power chip NCP1396 pin 12 power supply is normal, the oscilloscope measured PFC chip is already working, and NCP1396 did not work. The PFC voltage is connected to the 5th pin of the main power oscillation chip NCP1396 with undervoltage protection. It is estimated that the voltage is 0.8V. It is protected. Follow the foot to the PFC resistor R874 R875 R876R877. Check the PFC regulator loop resistance R826. R827 R828R829 R830 is also all normal. After the R829 is tested and the 47K resistor is used, the PFC voltage rises to 408V. The bifurcation may be caused by the PFC voltage drop caused by the high feedback voltage of the PFC chip NCP33262. The R826 R827 R828R829 R830 is removed again. The measurement is R805/563 (the drawing is marked as 0 ohm, there is a mistake!) The underlying glue has leakage, after all the glue under these resistors are completely removed, the PFC voltage is raised to 390V, and the PFC voltage is 365V after the backlight is bright. Then measure the voltage of pin 5 of NCP1396 to 1,2V. Nearly 6 test machines have not stopped.





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