Night attack Konka black screen new example - appliance repair

LED light-emitting diode

Yesterday, I got my hands on a Konka LCD TV model LED32F2000. The screen was completely black, but I could hear sound coming from it. When I used a flashlight, there was a faint image visible on the sides. Based on that, I immediately suspected a backlight issue. Before opening the panel, I decided to test the LED strip using a homemade LED tester I had built earlier. The result wasn't good — some LEDs were lit up, but others weren’t working properly. It was a bit strange, but at least I didn’t open the screen first, which would have made things much more complicated. I checked the original LED light bar from the store — a Konka LED32 fee 3300 model. When I turned it on, the light bar flickered very weakly and didn’t light up at all. This confirmed my suspicion: the problem was in the LED driver circuit. Since I was busy during the day, I decided to work on it at night. At night, I started by checking the power board and the LED driver board. The driver IC was an OZ9902CG. I tested the control pin (pin 3) of the 9902 and found it was at 3.2V, which indicated that the mainboard was sending a drive signal. However, when I checked the 13th pin — the overvoltage/undervoltage protection detection pin — it only showed 1V instead of the normal 2.5V. I then tested the sampling resistor R154, which was fine. Further inspection led me to check the LED power boost diode VD751. To my surprise, this diode had failed — it was shorted, which caused the boost circuit to malfunction. As a result, the OZ9902 detected an undervoltage condition and shut down. After replacing the faulty diode, the voltage at pin 9 of the OZ9902 returned to 2.5V, and the LED backlight started working again. I connected the TV to a signal source, and everything looked normal — the picture was clear and stable. I’ve attached a few photos for reference. You can also find my homemade LED tester in the career version section — go make your own!