A bit of guessing here. I suspect the APU was broken from the statement that Bay 53 had no power and wouldn't do.
So, if a 767 takes off from SYD then one of the generators on the engine breaks that would mean you are down to one generator and you can't fly more than one hour from a suitable airport.
If the APU was working he would have started that and used the generator on the APU and had two sources of power.
Before he leaves SYD he will have to get the APU fixed and/or the generator on the engine fixed, or what ever caused the problem.
