Kennedy,
I have a stupid question. Dallas, who like you knows approximately
7,428,321% as much about these machines as I do, once posted the message
below. I'm a bit lost reading (and even re-reading) it, but it seems to
imply there's a bit of ambivalence on some people's part about whether
it's advisable to unplug for CUDA resets, because of the possibility of
static-electricity damage to components.
Thoughts, anyone? Dallas, you out there?
--Tony
So many people have, shall we say, "embellished" the known to be
effective
procedures concerning CUDA & backup battery issues that it is starting
to become pure voodoo. Before this reaches the
sacrifice-a-chicken-while-holding-down-the-CUDA-button-at-midnight
stage, it seems like a good idea to separate known facts from
speculation. There is a real if small chance of damaging the hardware
with some of the suggested procedures, both from mechanical damage and
from static discharge, so let's
try to formulate solid rules about when and how to do what.
The problem is that Apple considers most details of the CUDA
microcontroller
propriatary so very little public info has ever been published. Only one
"official" article of any real use is available from Apple's TIL & that
came
from Power Computing. Apple will only say that it is "deemed accurate"
as of
late 1997. That article may be found at
(I don't need any URL trouble -- ask me for it if you're dying to know.
--Tony).
It isn't definitive and
there may possibly be some minor details that vary for SuperMacs, but
it's a
great place to start. I urge anyone wanting to contribute to the
discussion
to read it before posting vague info about CUDA resets.
The article does mention the "reputed" issue of battery removal for a
complete reset of the CUDA microcontroller. The implication is that it
is of dubious value but the good news is that it lists the exact
procedure to do it properly. The crux of the matter is to remove all
sources of power to the chip at once and give the machine time to
completely discharge any stored energy from circuit capacitance. That
means removing the battery & unplugging
the machine so the standby supply is disabled.
PLEASE NOTE that the main reason the normal procedures for working
inside the machine suggest keeping the power cord plugged in is to
provide a chassis-to-ground path for static to be completely dissipated
from the machine. (The ground pin on the ac cord provides a path to true
earth ground.) While the chances are small, even if you use a wrist
strap attached to the machine's chassis, it is possible to damage
circuitry with static potential if the path to true ground isn't
provided to drain off the charge. This is particularly important if you
are removing components such as DIMMs or PCI cards. It is well worth the
effort to provide that path whenever the machine is opened. The simplest
way to do that is to turn off a power strip with the ac cords of the
SuperMac & the strip plugged in in the normal fashion. (The power strip
switch in the off position kills the standby power supply just as
effectively as unplugging the SuperMac but maintains the ground pin
connection.)
I would like to draw readers' attention to one notable statement in that
TIL document that challenges conventional wisdom about when to hit the
CUDA switch (or do the battery removal version). It says that one reason
to do a reset is when adding any hardware to the machine BUT it suggests
that this should be done BEFORE adding the hardware, not afterwards.
This suggests a basis for the advice to remove DIMM's & such before a
reset but it also suggests that what is important may be to start with a
default configuration (if the microcontroller has stored corrupted
settings from some previous problem) or that resetting for each hardware
addition in one upgrade session is unnecessary or even
counterproductive. (That last sentence is obviously speculation on my
part.)
--
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