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

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Today, a customer sent in a Konka LCD TV with the issue that it wouldn't turn on. After opening the case and checking the power, I found that the fuse was blown. Based on my experience, this type of TV usually has a relatively powerful power supply. So, I started by testing the main components of the power supply. The test results showed that QF902, an N-channel field-effect transistor (model FDPF18N50), had failed. After replacing it, the 5V power supply came back to normal, but there was no voltage on the 12V and 24V rails. I checked the BC905 filter capacitor and found it charged to 300V, which indicated that the PFC circuit wasn't working properly. Further inspection revealed that the UF90 drive block (model FEK32) was damaged. Since there was no replacement part available, the fastest solution was to replace the entire board. I used a universal 205W power board instead of the original 170W one, and it worked well based on the data. However, when replacing the power board, there are some important steps to follow. First, always perform a no-load test before connecting the new board. Don’t rush — make sure all the cables from the original board are connected correctly. During the no-load test, you should be able to measure 12V and 24V power supplies after connecting the 5V PS/ON signal. Also, the high-voltage drive line must be properly connected. If not, the display might remain black because the CPU isn’t receiving the correct command to activate the high voltage. These key points are clearly marked in the images below.