On Feb 6, 2010, at 11:26 PM, Jim Scott wrote:
Try an Open Firmware reset of the video RAM.
snip
set-defaults
reset-nvram
reset-all
Just to head off future confusion, I'll be pedantic here.
This procedure dies NOT reset the 'video RAM'. That is volatile, its
contents go away when the computer shuts down.
the 'nvram' stands for 'Non-Volatile RAM', that is, stuff that stays
remembered between shutdowns, and is stored in special memory chips on
the computer, kept alive by the PRAM battery. (PRAM, stands for
'Parameter RAM' and is another name for NVRAM, as it stores the
parameters the computer needs to boot up to it's previous state,
hardware wise, like video settings, boot disk, and the current date
and time, when they're set differently than the defaults. If a Mac
ever gets past the initial boot stage (you see the gray apple or the
gear) the PRAM is not the problem.
This procedure WILL reset the video settings, so it'll work IF the
problem is that the display settings are set to something the display
cannot handle; however, I've never seen mis-set screens go all white,
they usually switch off...what typically happens is the computer
'bongs' the screen comes up, then immediately switches off. Some
monitors (the iMac screen does not do this afaik) will display a
warning that the signal is out of range.
Having to do things like this is most often a sign that the battery
that maintains these settings is dying. The lower than nominal voltage
makes it easier for the data in the nvram to get corrupted.
Some Macs will boot just fine without such a battery (at the cost of
having the boot volume, display settings and date and time reset to
the default every boot time) but most require that trickle of voltage
to turn on.
--
Bruce Johnson
"Wherever you go, there you are" B. Banzai, PhD
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