The Siemens 802D CNC controller shows ALM380500, ALM400015, ALM400000, ALM025201, ALM026102 and ALM025202, the amplifier shows ALM599.

Check the connection of I/O unit and outer 24V, and found there was DC24V at the connector, but it disappeared after going through the fuse F7.

Measure the fuse F7 separately, it is fine.

So this could be cold joint problem, re-joint the F7 fuse, then the Power and Ready lights of the I/O unit are on, all the CNC alarms gone, machine resumed