What happened?
The Original Prusa MMU3, as well as the MMU2S with firmware version 3.0.0 or higher, feature a voltage-sensing function managed by the Main Control Unit (MCU). This function monitors the 5V line, which supplies power to the logical components. It helps prevent malfunctions in the control board's components caused by an inadequate power supply. If the MCU senses insufficient power, the printer will display the message: "MMU MCU detected a 5V undervoltage. There might be an issue with the electronics. Check the wiring and connectors".
Error name: MMU MCU Underpower
Error code: #04307
How to fix it?
Access the MMU control board and visually inspect it for any incorrect assembly, surface damage, or cable damage. Try reseating the cables to ensure a proper connection. In the event of a poor cable connection, clean the mating surfaces of the connectors. In particular, make sure that the MMU3 PD-board add-on is attached to the control board.
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If the issue is not solved with these checks, please contact our customer support.