Finally, after many months of trying to get the backlight to blank, I've finally got it working.
There are two possible ways to get the backlight to go out: using the BIOS apm or using DPMS. Maybe they are related at some level in the BIOS but I could never find the common link.
Here's the BIOS settings I used:
PM Control by APM: No
Video Off Method: DPMS
Video Off After: Doze
Doze Mode: 10 Min
Suspend Mode: Disable
HDD Power Down: Disable
PM Events: All OFF, NONE, or Disabled
Primary INTR: ON
All others Disabled
I'm just letting the BIOS turn the backlight after 10 minutes. I was having trouble to get it to turn back on because I had the Primary INTR set to OFF. After looking at the VIA manual, it dawned on me that even though the keyboard was always set to reset the PM timer, the Primary INTR had to be set to ON to get that behavior.
So, after 10 minutes, the IO goes into Doze mode and turns off the backlight. Hitting the keyboard or the mouse brings it back on. This works great and doesn't stop any activity on the IO, unlike Suspend or Standby modes, which kill network activity.
I spent quite a bit of time trying to get DPMS working. When running as root, I got "xset dpms force off" to blank the screen, but I never got the backlight to turn off. When running as a normal user, "xset dpms ..." had no effect. I must have tried a million BIOS, kernel settings, etc. trying to get it to work. I even added:
to the Devices section of XF86Config but no luck. If anybody has a method to get the backlight to blank using DPMS, I would like to hear how you did it.
Among other things, I found out that having both ACPI and APM enabled in the kernel disabled APM and prevented the IO from powering down automatically at shutdown.
I found some good BIOS help at: http://www.phoenix.com/pcuser/BIOS/setup_index.htm where it explains a lot of the BIOS settings in detail.