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iMac G4 17" 1.25 GHz Model M9168LLA PowerMac 6,1 introduced in 2003.

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Why is my iMac G4 not powering up (after a power outage)?

Hi,

Our imac G4 is not powering up after a power outage during the night. It is connected to a surge protector. Other devices, connected to the same surge protector are working. We have tried the following:

1. turn off switch, unplug from surge protector, replug, turn on.

2. Take out power cord from the mac, and press the "on" button simultaneously while putting the power cord back in the mac. We waited for 10 seconds but nothing happened.

No sounds/smells.

Please help!

Thanks,

Barna

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Take out power cord from the mac, and press the "on" button and hold for 10 seconds. Now release the button and plug it in.

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Thanks you so much --that worked!!! But why did it happen? Should I get the mac checked out? Thanks again..!

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Glad this solved your problem. It's kind of like a heart, an electrical surge can stop or start it. After you reset your time, internet settings and printer settings, I wouldn't worry about it unless you find some anomalies.

The PMU Chip

The PMU (Power Management Unit) is a microcontroller chip that controls all power functions for the computer. The PMU is a computer within a computer. It has memory, software, firmware, I/O, two crystals, and a CPU. Its functions is to:

Tell the computer to turn on, turn off, sleep, wake, idle, etc.

Manage system resets from various commands.

Maintain parameter RAM (PRAM).

Manage the real-time clock.

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Thanks so much!:)

crwdns2893770:0crwdnd2893770:0crwdne2893770:0

So why did you unaccept my answer if it worked?

crwdns2893770:0crwdnd2893770:0crwdne2893770:0

So sorry! I clicked accept!!!!I I am going to change it! Apologies!!!

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Hard to tell from the distance, but all points to a dead power supply.

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Did it change to "accept"?

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There is a small reset button under the metal bottom plate next to the power test portals not far from where the AirPort Extreme card may be located. This usually would need to be pressed once, with the computer unplugged; not more than once between testing the startup since the PRAM battery may go flat otherwise. The button is hidden by sheet plastic, but can be activated without removing it.

Also, a reason why these may not start up after a power outage (without backup power supply) is the 1/2AA 3.6V lithium PRAM battery could already be dead, and this can make the computer fail to start. As this replacement is such a tedious task, it is not recommended unless you are going further into the computer and have skills, knowledge & abilities with this design.

Since most shops won't look at these anymore, work carefully and look for online guides, a few takeaparts to replace the HDD and optical drive exist. Thermal paste, and other tools are necessary. An original Apple Service manual on pdf is recommended, almost impossible to get.

Good luck & happy computing! :)

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It is possible that you could replace the battery ~$5, there are several guides here on iFixit, and one of them is a stinker, and some of the others are better. Anything that is 2 steps long is not detailed enough for non-experts. Once you replace the battery, you'll want to do the PRAM reset trick one more time.

This may be a long-shot though, even with my battery dead, I was able to get my iMac to boot sometimes, but I've seen Windows PCs stay dark until the battery was replaced... so, this step is cheaper than buying a new Mac!

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I had the same issue, and it turned out to be the PRAM battery. No combination of resetting with the power switch or the reset button near the AirPort card worked.

Pulled the PRAM battery, and even with 3.57 volts, I put an ammeter on it and it had a grand total of…….. 2 milliamps.

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I upgraded the drive to an SSD and again experienced the no start issue, even with a known good and tested PRAM battery. Again with different combinations of battery removal and board resetting, I decided to call it quits for the night with the machine unplugged. The next morning I decided to try one more time before harvesting the drive and CD, and wouldn't you know the darn thing started. I dont know why, but it could be the start circuitry on the MB that locked up and needs some time to 'reset'. I'm thinking that removing the battery first before doing any work that requires opening the machine would be a smart move, even if you're just replacing the drive.

Phantom253

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Reset the PMU. That should do it.

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I tried the 10 second unplug Thu g about five times

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