PRAM Battery Tip

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tmtomh's picture
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Joined: Dec 20 2003 - 10:38
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PRAM Battery Tip

Hi Folks,

Just had a first-time experience that I thought might be useful for people here.

I just received a very cool 5500 (actually, a 5500 board in a Color Classic, but that's irrelevant for this topic). Only problem was, the clock was off. Not only was it off, but the menubar showed 12:00AM, Jan 1, 1904, while the Date and Time Control Panel showed 6:28AM, February 6, 2040.

These are the earliest and latest dates+times, respectively, that a Mac of this era can display. But I'd never seen them displayed simultaneously!

In addition, whenever I reset the date and time, no amount of PRAM clearing or preference-trashing would make my changes "stick" after a restart.

Finally, I noticed that even through a PRAM reset, my custom mouse tracking and time zone settings would survive. And when I rebooted -- even after unplugging the computer from AC -- I never got the expected "Your Clock is set wrong" message when the desktop appeared.

I removed the PRAM battery and tested it. It read 2.2V -- about half the proper 4.5V (this is one of the square Rayovac ones, not the 1/2 AA ones).

Acting on a hunch -- and not having any full-strength batteries around -- I put a totally dead (less than 0.75V) battery in.

Lo and behold, the problem was fixed! I still have to reset the clock if I unplug the computer from AC of course. But the "Clock set wrong" alert appeared when I first booted after installing the battery, and now all my date and time settings "stick" properly.

So it seems that a half-dead PRAM battery can corrupt the PRAM and prevent the Mac from resetting the PRAM, or from recognizing that the battery isn't properly retaining PRAM settings.

Just an FYI.

Best,
Matt