How does level sensor work ？what's the detail principle of it?

Support & Troubleshooting
3

Thanks for your reply ! Sorry to reply after 18 h . We have done some works .We opened machine finally.

we have found the wires of the sensor connecting to the PCB but it has four wires, red blue white and black.Maybe there’s an unusual sensors in my machine ,

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I wonder if I can sove the problem by replacing a new resin senor.

And I tried to clean the board located the sensor but it didn’t work.A spot cannot be removed by isopropyl alcohol . I didn’t touch the sensor,but board.

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Or should I clean the board again? It seems dirtier than before ?!