LED backlight universal board replacement method example [Kangjia three-in-one board backlight transformation] - Home Appliances

LED light-emitting diode

A Konka LED26F2200C LCD TV was brought in with a backlight issue—no brightness, but sound was working. Upon inspection, it was found to have a three-in-one motherboard. The backlight circuit had several components damaged, including the boost diode, FET, and some resistors on the chip, causing the board to become blackened from heat. After repair, the user was advised to replace the entire board, though other parts seemed fine. Since the issue appeared to be isolated to the backlight, I decided to try repairing the original backlight circuit instead of replacing the whole board. There are various options available online for replacement backlights. One common type is a low-voltage power supply, which typically outputs around 24V or up to about 80V. These are suitable for boards that use a constant current voltage below 100V. Another option is a high-voltage booster board, which usually operates at around 100V or more. Many three-in-one motherboards have a separate 100V power supply dedicated to the backlight. These boards often drive LED strips with multiple LEDs in series, resulting in output voltages between 100V and 200V. To choose the right replacement, it's important to check the structure of the LED strip. Different models may have different voltages, but as long as the lamp bar voltage is known, a compatible backlight driver can be selected. A quick way to determine whether the backlight is low or high voltage is by checking the withstand voltage of the filter capacitor used in the constant current output. If the capacitor is rated at 100V, it's likely a low-voltage setup. If it’s rated at 250V or higher, it’s probably a high-voltage system. High-voltage backlights can often reach over 200V when measured without load. Here are some examples and photos from the repair process:

This is the original three-in-one motherboard.

Removed the damaged components from the booster section, while leaving the rest untouched.

Located the 12V, 100V power supply, and the backlight control signal lines.


Identified the control wiring and connections.

The original light bar was connected in two series groups to maintain the same performance as the original.

Ensured all wiring was correctly connected.

After installation, the operating voltage of the light bar was measured at approximately 125V. The brightness varied slightly depending on the voltage.
Successfully lit up the screen, and the result was nearly identical to the original unit. [attach]421519[/attach][attach]421518[/attach][attach]421517[/attach]