Error on the remote display of the black box Headway HMT.  This error indicates a power failure of 220 V. The Black box also fits 24 from the ship's batteries / power supply and from its batteries inside the power supply, so the work continues.  

This model of black boxes has a separate power supply.  At the bottom of it, 220V AC and 24V DC are connected. It is necessary to disconnect 220 and check the voltage in the cable. if not - look where the cable is coming from and check the source. If the voltage is - remove the cover and on the board on the bottom right, where the AC 220 wires are connected there is a fuse - check it.  

The work must be performed by a qualified engineer, it is better to call for service on board to prevent equipment failure