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 supplying the logical components with power. It helps prevent malfunctions in the control board's components due to 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 inspect it visually to spot any incorrect assembly, or damage on its surface or damage to the cables. Attempt reseating the cables to ensure their connection. In case of poor cable connection, clean the connectors mating surfaces. In particular, make sure that the MMU3 PD-board add-on is attached to the control board.
If the issue is not solved with these checks, please contact our customer support.