Hmm, I will guess...
Since it's dealing with power issues, I would check all fuses and be sure they are ok. When power comes back on, it can spike. Be sure the voltages are reading as described in your maintenance manual. Once you have ensured the system is getting correct voltage AND amperage in "all" its respected circuitry. Move on to each issue and try to isolate them.
Take your time, and try not to overlook anything.
You could attempt to go through the initial installation sequences as if the machine was new.
That's what I would do to get an idea of what was going on with any failing piece of equipment.