Beckhoff · EL6900 Operating Instructions
This diagnostic code (found within FA00:03 Supply error) indicates that the supply voltage to the secondary microcontroller (μC2) has fallen below its minimum permissible limit. Similar to μC1 undervoltage, this condition can cause unstable operation, data corruption, or unexpected shutdowns, impairing the terminal's safety and reliability.
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Measure the input supply voltage to the EL6900 terminal using a multimeter at the power terminals.
Verify that the external power supply unit providing power to the terminal is operating within its specified voltage range and can supply adequate current.
Inspect the power supply cables and connections for any signs of voltage drop or loose contacts.