Hi Charles, Thank you very much for your reply. And I'm sorry for reply so late, we went to a conference for several days. The schematic is as follows: And we takes all the main chips off the board, and find that: 1. The VSS( -5V ) of LM96530 is short to GND 2. The VLL( 3.3V ) of LM96551 is short to GND We don't know why these two chips are damaged. And we have a question: when the power supply is off, should the output of the supply be 0V or be open circuit? For our switch board, the output is open circuit when the switch is off. And we think the direct ouput for a power supply may be 0V when it's turned off. Thank you. Yours sincerely, Frank
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