Hello IanB,
I had just clean the switch, it seems that is not a sw problem. My Casioton 701 has not been used for some years, when i conecte it laste week the two 0,002 micro f capacitores includede in the power supply unity burned, i had just replaced them.
I am interested in fault fiding iam a little familiar with electronic but dont have big experience with electronic fault fiding but can try.
Do you have the electric diagram of 701?
Thanks for your support
Regards,
Antonio Neto
Sorry for my English, iam Potuguese.