Hisense LCD TV 42K431DX4F automatic shutdown fault repair example - appliance repair - Database & Sql Blog Articles

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The Hisense 42K431DX4F LCD TV is experiencing automatic shutdown issues. After checking, the PS-ON/OFF voltage was found to be 0V, indicating a potential problem with the motherboard. Further inspection revealed that the CPU power supply was not providing the expected 1.25V. Checking the DC-DC circuit for the CPU, specifically component U5, showed some irregularities. A diagram of the circuit was taken for reference.

During testing, the voltage at point C increased from 0.8V to 2.7V. When point C reached 2.7V, point D stabilized at 1.25V, and the CPU functioned normally. However, during the fault condition, point A remained at 5V while point B dropped rapidly and then slowly rose. This behavior suggested an issue with diode D3. Replacing D3 resolved the problem, and the TV returned to normal operation without further issues.

This repair process highlights the importance of careful voltage monitoring and component testing when diagnosing power-related faults in electronic devices. It also demonstrates how small components like diodes can have a significant impact on overall system performance.