Power outage, electrical spike issues and the Mac's CUDA switch

We recently posted a link to discussion (see the "Forum Hot Topics" section below) in the MacFixIt forums regarding problems that arise from electrical storm spikes and power outages.

In many cases, when Macs will not power up properly or display other issues after an electric irregularity, you can regain full functionality by pressing the CUDA switch. The CUDA is a microcontroller chip that - according to Apple - performs the following functions:

• Turn system power on and off
• Manage system resets from various commands
• Maintain parameter RAM (PRAM)
• Manage the real-time clock

On most machines, the CUDA reset button is located to the right of the system battery.

Pressing the CUDA switch resets all data (PRAM, NVRAM, clock and other) stored in the microcontroller. Essentially, pressing the CUDA switch is the same as removing the battery.

One user writes "The power went out in our town yesterday and went it came back on my iMac that i have set up as a server would not restart. After pressing the power button the first time after the electricity was back up, the iMac shut off after half a startup chime. Then nothing. [...] I then tried a series of removing the battery, and replacing the battery. The power switch lit up for a second then died. I gave it up for dead, then tried pressing the CUDA switch, and it was fixed."

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