All recent DIN rail modules are equipped with a fuse and status LED(s)
In the first place, it must be checked whether the upper PWR LED is still lit (green). If this is not the case, check the fuse and check the supply voltage. If both fuse and supply voltage are correct, then the module power supply is defective and must be repaired or replaced.
Be sure to try a complete reset first: interrupt both the voltage and bus simultaneously, then reconnect voltage (and possibly bus).
Use our RMA procedure to return a module
The lower PWR will light when the bus is connected correctly. In stand-alone mode, this PWR LED, therefore, remains OFF. The red status LED will briefly light up or flash when the module is started. But if it remains lit or flashing, the firmware may be corrupted. Updating the firmware can be done via the SMIII via “Utilities / Setup / Software / Modules: Firmware Upgrade”