I have just started to use TinyCore and I have a similar problem with auto sleep coming on when not required, I need the monitor on all the time for the application that I am using (displaying an Openscenegraph model).
I have entered in : xset s off at the command prompt, however the auto sleep remains on and the system goes to sleep after a period (wakes up on a keyboard press). I have also added xset s off to /opt/bootlocal.sh and ~/.xsession and restarted (with a backup), but again the system goes to sleep after a period. The /opt/bootlocal.sh file still contains xset s off however the ~/.xsession file does not (both were edited using sudo).
I am using TinyCore V4.0 and I have also installed the ati-fglrx and ati-catalst packages for the graphics card I am using (which all work okay).
Any further help will be useful, thanks.
Terry