Konka LCD TV LC37FS81C three trouble-free replacement board repair example - appliance repair - Huaqiang electronic network

Today, a customer sent in a Konka LCD TV with the issue of not turning on. After opening the case and checking the power, we found that the fuse was blown. Based on experience, this TV has a relatively high power supply, so I first tested the main components of the power section. The test revealed that QF902, an N-channel field-effect transistor (model FDPF18N50), had failed. After replacing it, the 5V power supply worked normally, but there was no voltage on 12V and 24V. We checked the BC905 filter capacitor and found it charged to 300V, which indicated that the PFC circuit wasn't functioning properly. Further investigation showed that the UF90 drive block (model FEK32) was damaged. Since the original part wasn’t available, the fastest solution was to replace the board. We used a universal 205W power board instead of the original 170W one. It turned out that the power was sufficient for the system to run. However, when replacing the power board, there are a few important steps to follow. First, always perform a no-load test before installing the new board. Don’t rush into connecting everything. Also, make sure to check the cables from the original board and connect them correctly. During the no-load test, you should be able to measure 12V and 24V by connecting the 5V PS/ON signal. Additionally, the high-voltage line must be connected properly — if it's not, the display will remain black because the CPU isn’t receiving the necessary command to activate the high voltage. These key points are clearly marked in the images below for better understanding.