One L46E9FB [MS58 movement], the motor does not react, the power indicator light does not light, the initial judgment is "no power". 4 Inch Driver,4 Inch Neodymium Driver,4Inch Voice Coil Driver,4 Inch Coil Horn Driver Guangzhou BMY Electronic Limited company , https://www.bmy-speakers.com
The inspection found that the sub power supply 3.3V is 3.4V, which is normal. The 3.3V sent to the receiving head and the indicator board is also normal. The power supply PS-ON is 3.5V normal. The backlight BL-ON is 0V abnormal, and the main power supply 24V is 0V. The main power and PFC chips of this machine are IC6 [NCP1396] and IC1 [54B65] respectively.
Analysis: Since PS-ON is normal, then the PFC and the main power supply should work normally. The voltage across the large electrolysis is 350V. Normally it should be about 400V, which is slightly lower. Since the PFC can work, although the output is low, it means that the power-on voltage is normal. Is the main power supply not working because of the low PFC voltage? With this idea, check the IC6 [5] foot voltage detection pin is 0.8V, and the data should be above 1.2V, which proves that the undervoltage protection is caused by the low detection pin voltage. Recall the IC1 voltage feedback pin [6] external voltage divider resistor R10,11,12,97 value, found that R11,12 was originally 105, the measured 800K or so and unstable, pay attention to prevent the soldering iron heating fault component self-recovery To cause misjudgment, the method of cutting the relevant copper foil is adopted. After switching on two chip resistors of the same specification, the PFC rises to 400V, the main power supply works, and the picture sound is normal.
Summary: As the voltage divider resistance of the PFC feedback circuit becomes smaller, the voltage of the FB of the IC1 [6] is increased, and the output voltage of the PFC is lowered due to the voltage regulation. The voltage drop detected by the pin of the main power chip IC6 [5] causes undervoltage protection. The main power supply stops working, and the main board CPU does not detect the 24V sent from the power supply board and turns off the BL-O.
During maintenance, did you notice that due to the different settings of the undervoltage protection, some of the PFCs do not work or the PFC voltage mentioned above drops, which will cause undervoltage protection, while others will not work even if the PFC is removed. It depends on the presence or absence of the undervoltage protection circuit and the setting of the undervoltage protection voltage value in the circuit design.
Therefore, in the actual maintenance, if the PFC circuit fault is complicated and cannot be solved, the LED backlighting machine can skip the PFC circuit because of low power consumption. If it can not work normally, the voltage divider resistance of the main power supply voltage detection pin can be changed. The value is such that it satisfies the voltage range specified by the chip data. For LCD backlights, especially for early models, due to the large power consumption, less PFC will cause the main power consumption to increase, and the temperature rise will become higher. For the sake of reliability, commercially available PFC modules or replacement boards can be used to solve the problem. [attachimg]538855