1, what is the PFC circuit? PFC circuit that white is the bridge after the rectifier +300 V voltage increased to +375 V ---- +400 V. This is also the LCD TV LCD Power Bank and CRT TV power of the difference between the first point, the difference is that the secondary voltage is lower than the CRT, the other places with the same general principle of switching power supply are the same. Measured the filter capacitor 330U / 450V voltage is +375V --- +400 V, then the power factor correction circuit is working properly; if the measured voltage across the capacitor +300 V, indicating that the PFC circuit is not working, the main check PFC oscillation integrated circuit.
2, maintenance of LCD Power Bank, the first to confirm the state of the fuse, the fuse is intact, usually PFC correction circuit switch tube does not fail. And then measure the large electrolytic capacitor to the ground whether there is a short circuit, there are dozens of ohm above the charge resistance, indicating that the power is not breakdown. If the fuse is damaged, the first one should check the PFC correction circuit switch and the second to check the secondary power IC. ;
3, 40 inches below the general output + 5V, +12 V, +24 V three sets of voltage; 40 inches above the general output +5 V, +12 V, +18 V, +24 V four groups of voltage. Which +5 V for the standby voltage, +12 V for the digital board, +18 V for sound, +24 V for the backlight board. In the practice of maintenance, as long as the voltage of each group, the power of the same power board can be replaced.
4, the LCD Power Bank board can be removed from the TV on the independent maintenance, maintenance only need to switch the circuit control circuit transistor C, E short (or a resistance of about 1.5K and secondary power supply + 5V output connected) The machine is in the boot state, the voltage is output. In some LCD TV switching power supply, only +12 V or +24 V output with a certain power load, the main switching power supply to the normal working condition. So at the +24 V output you can take an electric bike's 36 V bulb for a dummy load (or a + 6V output with a motorcycle light bulb). The