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The Necessity Of Maintenance Of LCD Power Bank Dummy Load

Repair a lightning hit Skyworth 37M11HR TV, power board 168P-P37TTF-01, failure: red light, the second boot after three no, crash. LCD Power Bank load without short circuit phenomenon, pick the power board alone repair, repair 12,24v basically did not take the dummy load. Forced to start, test 5v normal, no 12,24 v, the power board on the relay without breathing sound, measured relay no working voltage, along the road to find the standby circuit of the coupler breakdown, Q3 / Q4 breakdown caused by optocoupler no bias Voltage, replace the bad parts, power, relay pull, but still no 12,24 v, strange in the power of a few seconds instant 12,24 v there, low. Protected! Carefully observe the circuit board and found that 12,24 v are no drawings marked on the ground resistance, it would not be no load it! Connected to the dummy load, long absence of 12,24 v finally have, on the machine, all OK!

Example shows that not all the power board can be no-load maintenance, in the decision not to use false load, to see if there is no load on the board to the ground resistance, there is no need to take a fake load.

(12V, 24V, etc.) into 500-1000V high-frequency high-voltage, the use of the backlight to use the tube. The main tools for overhauling high voltage inverter circuits are oscilloscopes and multimeters. Because the high-voltage inverter circuit operating frequency is high (50-80kHz), so you can use the oscilloscope to measure.

In the case of

Multimeter can use ordinary high resistance mechanical pointer table (such as the commonly used MF47,500 type) and digital multimeter. It is emphasized here that the internal resistance of the multimeter is high enough to avoid the influence of the circuit under test (affecting the operation of the circuit).

In the case of

(2) In order to ensure the balance and reliability of CCFL LCD Power Bank, LCD color TV high voltage board circuit uses several groups of exactly the same circuit, respectively, for each light LCD Power Bank. Maintenance can be compared with each other, due to the possibility of several groups of circuits at the same time almost no damage.

In the case of

(3) LCD TV backlight power circuit with high-voltage balance protection circuit, through the high-voltage output current detection to determine whether the normal high pressure. If the high-voltage output current is unbalanced (for example, if a backlight in a multi-backlight system is damaged and badly connected, any high-voltage output circuit components are damaged), the circuit is judged to be faulty by the inverter control IC Oscillation circuit stop vibration, turn off the high voltage output. At this time as follows: the screen flicker, and then become "black".

In the case of

For models that do not have a high-voltage balance protection circuit, there will still be a faint image display on the side of the screen after a high voltage circuit failure. Through this feature can quickly determine the fault appears in the high voltage circuit.

In the case of

(4) backlight LCD Power Bank circuit also has a brightness adjustment interface, the interface by the MCU issued by the brightness adjustment PWM pulse control. This interface voltage changes, will change the high voltage output value, it will change the brightness of CCFL, LCD TV to achieve the brightness adjustment. If this circuit is normal, adjust the brightness of the interface voltage will be smooth high and low changes.


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