A quick thread-ender:
The CUDA Reset button is a small red button located on the Main Logic Board.
For more
information on the button's location on the various Power Computing
models, please see the
following Tech Info Library article:
Article 36253: CUDA Button Location and How to Get to It
Definition:
===========
Depressing this button resets the CUDA Microcontroller Chip. This chip
is responsible for the
following functions:
* turn system power on and off
* manage system resets from various commands
* maintain parameter RAM
* manage the Apple Desktop Bus (ADB)
* manage the real-time clock
* let an external signal from either Apple GeoPort serial port
control
system power
CUDA is powered by the Motorola power manager chip which draws power
from
1) the 5V rail if power supply is turned on,
2) the 5V standby supply if the power supply is plugged in but not
turned on,
3) the battery otherwise.
When you push the red button, it makes no difference whether you are
plugged in or not. If you
are turned on when you push the button, the CUDA is reset which will
turn the machine off.
Though it seems incomprehensible from an engineering standpoint, there
are reputed to be
problems with CUDA that require the battery be removed to completely
kill it. In this case, you
must unplug the line cord or CUDA will continue to be powered by the
5V standby supply. It is a
good idea to leave the battery out for 10 minutes or so, since it may
take that long for all of the
stray capacitance to discharge, etc., and put it in a truly
uninitialized state.
There is a difference when the line cord is plugged in (5V standby
active) in that CUDA runs in
so called "high power mode" which involves faster clock rate, more of
chip powered up, etc.
Though the spec. doesn't say so, this may account for some
peculiarities.
When to Reset:
=============
It is rarely necessary to reset the CUDA, but many problems that
appear to be hardware related
can be fixed by doing so. Some of the most common reasons to reset the
CUDA:
*After adding RAM, the machine will not boot.
*The machine will not power up.
*The machine powers up, but does not chime or boot.
*A serial port remains inaccessible even after booting without
extensions,
resetting PRAM, etc.
*The machine will power down for no apparent reason.
*Before adding any hardware to the inside of the machine.
Of course, normal troubleshooting steps should be taken to resolve a
problem before resetting the
CUDA. Although resetting the CUDA will not harm the machine in any
way, it is important to
remember that most problems can be resolved without opening a machine.
How to Reset:
=============
*Power down the machine, but leave the power cable plugged in.
*Remove the cover.
*Locate the CUDA Reset button.
*Touch the metal chassis of the machine. This will dissipate
static
electricity
into ground.
*Press the CUDA button for a few seconds.
*Reboot, and verify resolution of the problem you wanted to solve
Although it is rarely necessary to do so, the CUDA microcontroller can
also be reset by removing
the lithium battery and unplugging the machine. If you choose to do
this, the machine should be
left unplugged with the battery removed for 15 minutes to allow all
stray charge to dissipate.
Information on the functions of the CUDA Microcontroller was taken
from the following Tech
Info Library article:
Article 14841: Power Macintosh: Description of Integrated Circuits
Machines Affected: All
; )
Mark Vaillancourt
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