Sharp PC-1403H stuck on "BUSY"

[Dave Britten]

I know we've got some Sharp fans here, so I figure it's worth asking. I acquired a PC-1403H that's in very nice condition, apart from the fact that it doesn't seem to work! When I insert new batteries and power it on, it just displays the "BUSY" indicator and can't be turned off again unless I turn off the power switch and press the All Reset button on the back.

I opened it up and replaced the lone electrolytic capacitor and cleaned the power switch contacts, but that didn't seem to change anything. Anything else I should check? Does this model have a self-test feature?