If the indicator on the 6442 mainboard does not light up (the indicator on the KN332, however, is nestled in the middle of the mainboard, so it might be hard to find), check whether the low-voltage power supply lights up.

• If the power supply does not light up, follow the procedures in"Switch power supply indicator not lighting up".
• If the switch power supply indicator lights up normally, but the mainboard indicator still won’t come on, measure the input voltage of the mainboard (as shown in the video, with the mainboard power supply plug plugged in and unplugged).

• If the mainboard voltage is always 24V, then the mainboard is faulty. Replace with an identical one.
• If the voltage remains 24V when the plug has been removed and does not when the plug is inserted,

1. Remove all the plugs on the mainboard except the power supply plug and measure the voltage of the power supply plug again.
2. If the voltage of the power supply plug of the mainboard returns to normal after removing all the plugs on the mainboard, it means that one or more of the accessories connected to the mainboard were short-circuited.
3. Plug back the plugs on the mainboard one by one to find out which of these accessories is causing the problem. (Accessories that may be problematic include: the X/Y axis limit, the autofocus sensor, and the open-cover protection sensor)
4. If you have sorted out the possibility of a faulty plug and the voltage of the power supply plug of the mainboard is still abnormal, replace the board with an identical one.