The Linux console tty implementation supports a "VESA blanking mode" option. This appears to define whether "console blanking" will actually standby/poweroff the monitor (presumably via DPMS) rather than just clanking out the screen while leaving the monitor on.
This is set via the
TIOCL_SETVESABLANK ioctl which is (incompletely?) documented in
ioctl_console(2) and is used to implement
--powersave option. That's all reasonably clear.
This value appears to be initialised by the kernel to
0, or 'none', i.e. don't turn off the monitor. But experimental evidence on two very different distributions (Debian and Gentoo) suggest that, with the kernel
consoleblank (automatic blanking interval) parameter set, the monitor does get turned off -- which implies that this VESA blanking mode is set to a value other than
0. Unfortunately there does not appear to be any easy way to read this setting back, so this experimental evidence is all I have.
If this supposition is correct and the VESA blanking mode has been set to one of the other values - where has it been set? Which component has changed it from the kernel-initialised default? Can it be configured?