Thank you Robert. I wouldn't have known about xset. After reading the man pages, I believed that "xset s noblank" would do the job. Opened a terminal and tried it - no error or any other messages. The screen still blanked. Su to root tried again, same result.
Rebooted just to be sure and timed it with an outside clock: in 10 minutes, the screen blanked. In another 10 minutes the screen saver came on. The screensaver is set to come on in 10 minutes.