@Truck
ah, right, the Japanese MSX you mentioned was for a different person :)
Yeah, sounds like it was just the RTC batteries then. With a bit of luck they haven't done so much damage already that it can be replaced with a button cell (and probably one of those one way resistors so the machine won't try to charge the button cell). I'll check tomorrow when I'm at my laptop again if I can find a guide for you/Dozer.
Not sure if the #NMS8245 also offers the option, but the #NMS8250 also had a jumper in the form of a soldered rod that allows you to set it to 240V rather than 220V; that should help reduce some heat production with current level of mains power. I'll ask if that's also the case with this model.