Operation method for judging LED light string faults using a clamp table
After repeated experiments, it was found that using a clamp meter can accurately determine the fault of LED light string. The specific operation method is as follows:
Step 1: Determine the number of LED groups and the+and - lines inside the screen based on the wiring of the LED light string. For example, the wiring diagram of the LED light string of a 39 inch LED LCD TV shows that there are 5 sets of LED light strings inside the screen, and the wires marked with "+" are connected to the positive pole of the LED light string, commonly known as LED+wires; And the corresponding wiring marked with "-" is connected to the negative pole of the LED light string, commonly known as the LED line.
Step 2: First place the clamp meter in the minimum range of DC current, and then clamp the clamp onto the LED+or LED - line of the LED light string.
Step 3: After powering on, turn on the machine for the second time and observe the reading of the clamp gauge at the moment of powering on. If the faulty machine has multiple sets of LED light strings, it is necessary to turn on the machine multiple times to measure each set of light strings and record the current readings of each set of light strings.
If the current reading of a certain group differs significantly from that of other groups (the fault phenomenon is mostly that the backlight turns off immediately), check the wiring, plug, socket, and peripheral circuit of the LED terminal of the group of light strings for abnormalities. If it is normal, it can be determined that there is a problem with the group of light strings; If the current readings of each group of lamp strings are similar and far below the normal value (the fault phenomenon is mostly black screen), it indicates that the backlight drive circuit is abnormal.
If it is determined that the fault is caused by an abnormal set of LED light strings on the screen, the LCD screen can be disassembled to locate the set of light strings, and the diode block of a clamp meter (or digital multimeter) can be used to measure the forward voltage drop at both ends of each LED on the set of light strings in sequence. Normally, the measured LED beads will emit weak light, and the forward voltage drop of each bead is not significantly different. If the positive voltage drop of a certain lamp bead differs significantly from the others, it indicates that the lamp bead is broken.
