There are several reasons why Sharp chose to use three separate supplies.
One was to minimize the cost of a building a single "rilllly big" supply.
The other is that it wanted to minimize the amount of bypassing and
decoupling needed on the boards.

The obvious answer to the question of why the set didn't work is that it
doesn't "like" being driven from a single supply. (The original supply was
likely missing because the was tossed out as defective (for whatever unknown
reason)).

I would not have plugged a single supply into it, simply on the (admittedly
remote) possibility that it might be damaged.