You can turn it off with the little switch inside the
main batter
compartment. The machine should run from the main battery
(or a 5V PSU connected in place of the main battey) if there
are no otehr problems.
Both of my PX-8s (an earlier and a later model) will run with the 6V
wall wart connected into the proper socket when the main and wedge
batteries are removed. I wouldn't exactly recommend bypassing the
little bit of protection the charger input provides.
Josef
--
"I laugh because I dare not cry. This is a crazy world
and the only way to enjoy it is to treat it as a joke."
-- Hilda "Sharpie" Burroughs,
"The Number of the Beast" by Robert A. Heinlein