Oh that's a pity. Unfortunately we do not have a Casio repair centre now, although we had one those years ago when I had the speakers repaird. It seems the consumer culture is the thing - chuck it away and buy new.... but i don't want to do that if I can get around it, so I will try that suggestion of leaving it on. Normally I turn it off at the wall as well as on the machine.
The problem with the missing tones, is that one of the registrations, which I used a LOT, no longer plays the accompaniment, so I have had to fiddle around to get an alternative for that particular registration, but because that has happened, I thought it might be the precursor to the keyboard failing in other registrations too. This is really why I bought the digital piano, as it also has a lot of the pre-set sounds and rhythms of the MZ2000, so I can get used to it, although I am not a pianist, and find the touch not as easy as the keyboard. No doubt I will get used to it, if I persevere?
I really appreciate your taking the trouble to reply.