Can anyone please help me with my Casio WK-1200 Keyboard problem. I have totally lost sound but every other function appears to be OK.
I was hoping to find a way to attempt to re-set the device, but I can't find any way from the manual, or from the Net

Try asking this on the Synth Zone Casio Forum . Jim Wintringham often is able to help and may be able to suggest a solution.

Check your local off setting in midi paramaters...this disconnects the keys from the sound source..

SUCCESS!!!

I've figured out the problem to my Casio SK-1200 no sound issue.

It is something to do with the MUTE. I never bothered to find how to un-mute mine, I simply bypassed this feature by soldering a jumper on the LA4620 amplifier (big thing connected to the big heatsink). By applying 12Vdc to the pin 13(I jumped pin 11 to 13 since they're next to each other), the mute function is disabled.

Here is the link to the LA4620 manual http://pdf.alldatasheet.co.kr/datasheet-pdf/view/40130/SANYO/LA4620.html

Good Luck!