1. LED backlight panel maintenance
Compared with CCFL backlight board circuit, LED backlight board circuit has no AC high-voltage output and outputs DC voltage, so the maintenance of LED backlight board is simpler.
When LED backlight panel is repaired, there is a big difference between the output voltage with and without load. For example, the output voltage of 4a-lcd32t-auc screen backlight board is 57V when connected with load, and 120-140v when not connected with load; the output voltage of 4a-lcd55t-ss1 Panel two in one power supply board connected with load is 200V, and the output voltage without load is 125V. Pay attention to the difference between the load with and without load during maintenance.
LED backlight board generally has several groups of voltage output, each group not only has the same output voltage value, but also has the same circuit components and circuit composition. Therefore, when repairing one of them, you can refer to other branches.
General LED backlight circuit input voltage is 24 V, small screen is 12 V, so as long as the output voltage is the same, there is the possibility of replacement.
2. LED light bar maintenance
Generally, a LED LCD screen has multiple groups of LED light bars, some have four groups of LED light bars, some have six groups of LED light bars, and several groups of LED light bars on the same screen are the same. There are multiple LEDs on each LED light bar, and each LED is welded
The process is assembled on a metal strip.
If a group of LED lights are not on during after-sales maintenance, the resistance value at both ends of each diode can be measured with a multimeter, which can neither open circuit nor short circuit. The working voltage of some diodes is about 3V or lower. For example, the working voltage of 4a-lcd32t-auc screen diode unit is 3.2V. For such diode, when the resistance is measured with RXL gear or rx10 gear of pointer multimeter, the diode will emit light. Some diode units have high working voltage at both ends, such as 4a-lcd55t-ssi screen diode unit. There are two series diodes integrated in it, and the working voltage is 6.5V. When measuring the resistance value at both ends of the diode unit with a multimeter, the diode will not emit light, but there is resistance value.
Generally, if the whole LED is on, it is necessary to judge whether the whole LED is open.
3. Troubleshooting of LED backlight panel
(1) No light and flicker when starting
In this case, first check whether the connection between the LED backlight board and the screen is correct. If it is normal, check the backlight board circuit. The necessary condition for the backlight panel to work normally is that the power supply (generally 24 V or 12 V), enabling end and brightness input end are normal; if the above detection is normal, then check whether the fuse is damaged, whether the driving switch tube is damaged, and whether the energy storage inductor is short circuited. According to the maintenance experience, the main vulnerable parts are driving switch tube, energy storage inductor, etc.
(2) Dark block appears in a certain area of LCD screen, or regular indirect dark block
In this case, the light bar is not lighted, and the light bar or backlight board is abnormal. During maintenance, it is generally necessary to check whether the circuit related to the light bar is normal. If it is normal, there may be led open circuit, short circuit or abnormal connection line and socket in the lamp string.
(3) It will go out as soon as it is turned on
In this case, the protection circuit may be triggered. Generally, the LED light bar is open circuited or short circuited, and the driving switch tube leaks electricity. It may also be the fault of the protection circuit itself.