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Thread: PMU reset - careful there!

  1. #1
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    From MacIntouch 4/1/2002:
    <BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Dave Andrews reminded us of an important warning about logic-board reset switches in recent Macs:

    "I would like to draw your readers to the nature of this logic board reset switch! This reset button is the PMU manager reset (Power Management Unit) [and it] controls power management funtions like the real time clock, sleep and resume, automated start and shutdown etc. Pressing the reset causes the PMU to reboot; pressing it twice can crash the PMU! You should press this switch only once, then wait ten seconds then boot up as normal. If the PMU crashes it is possible that the PRAM battery will be exhausted, lasting just 2 days once the power is removed, instead of it normal 5 years. ACSE engineers are taught this on Apple Training, yet I have been unable to find a TIL (knowledge base article) detailing this level of info. The TILs just warn against pressing the button just once, yet don't say what happens if you press it twice and crash the PMU. Note resetting the PMU differs on various models - G4s you hold the button for 1 second, TFT iMacs you simply press the button once." <HR></BLOCKQUOTE>
    Something to keep in mind...

  2. #2
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    Darn Gregory,

    I have read quite a few manuals that talk about the PMU in iMacs, first I've ever heard it mentioned in relation to G4s. No simple CUDA switch anymore huh? Guess I'll have to do some manual research, would hate to cause such a failure.

    Rick

  3. #3
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    Rick,

    I don't know when or if all PNU units suffer from this, but I do know there was talk about having to use it on the new iMac flat panel to fix a problem. So it may be present in the QS also. Apple really needs to spell it out and come out with something in the public knowledge base (I've noticed stuff get pulled so I try to check the "what's new" every morning).

    This is stuff that we here and folks on other upgrade forum sites need to know. "Sad Macs" 5th or 6th edition in sight? That use to be a good place to look to help out for troubleshooting and upgrading.

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