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A possible fix for a Mac that won't power up System
I have a client that has a Mirrored Doors G4. When you pressed the power button, the button would light up, but the computer would not turn on.

Initially I thought it was a power supply problem, as the fans on the power supply wouldn't turn on. I assumed there was enough voltage to turn the light on, but not start the computer.

So I tried using a spare power supply. Still it didn't work. Uh oh, motherboard problem maybe....

Then, on a hunch, unplugged the machine, pulled the clock battery, hit the power button to discharge. Then plugged it in without the clock battery. The machine booted perfectly. I shut down, reinstalled the clock battery, and now the system is fully functional again.
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A possible fix for a Mac that won't power up
Authored by: Hanji on Apr 11, '05 01:05:18PM
I had a mac with the same problem once, tried resetting the PMU, swapping the battery, and all that, to no avail. I was just about to send it in, until I tried a reboot without any peripherals, and lo and behold, it turned out to be this thing, which I'd just plugged my iPod into (with the dock cable plugged into the back of it), which was somehow keeping the computer from powering up. Short or something, I'd guess, but it was completely reproducible, as I found out the hard way.

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A possible fix for a Mac that won't power up
Authored by: gerbercomplex on Apr 11, '05 01:24:25PM

Most of the Time its is alway the PMU RESET Button. it always works (except for the one bondie, but that was the power supply) its very tiny and does the same thing as removing the clck battery, ust its not a likely to kill the battery.



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A possible fix for a Mac that won't power up
Authored by: tetsuotheironman on Apr 11, '05 01:20:15PM

this was a problem with your 'PMU'..
occurs freqently when there is a power disruption in your area..

there is also a small button on the logic board that would do the same thing.



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A possible fix for a Mac that won't power up
Authored by: randydarden on Apr 11, '05 09:20:52PM
"there is also a small button on the logic board that would do the same thing"

On my machine, at least, this is called the "CUDA switch." Search Apple help for more information. Reportedly, pushing it more than one in a power cycle will render your computer useless!

I have a G4 Quicksilver 2002 that almost never powers up from a cold start -- I always have to open it up and hit the CUDA switch. From what I've read, it's a problem with the logic board or the power switch board, and would have been replaced under warranty had the problem shown up soon enough.



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A possible fix for a Mac that won't power up
Authored by: johnsawyercjs on Apr 14, '05 06:43:52AM

Try a new clock/PRAM battery--you can get them at Radio Shack.

If that doesn't fix it, it may be a problem with the front panel circuit board.



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A possible fix for a Mac that won't power up
Authored by: sophistry on Apr 11, '05 01:41:54PM

Yes, I had this same thing happen on my mirrored door G4. And I found the same solution. All I did was put a new battery in. Thanks for posting this.

I think there was something on the Apple website about it recently - something to do with the battery draining because of some power surge or improper shutdown...

---
soph



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A possible fix for a Mac that won't power up
Authored by: Mac112 on Apr 11, '05 02:13:06PM

I have rescued dozens of G4's with this symptom by simply unplugging the power cord, removing the battery, counting to 10, reinserting the battery and power cord - and booting.



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A possible fix for a Mac that won't power up
Authored by: lirapd on Apr 11, '05 04:51:59PM

It's a good idea to always check the voltage on the battery because of the discharge curve on Lithium ion batteries. The drop off is rather steep as compared to a alkaline type which drops off gradually. Since the motherboard doesn't draw that much power, simply warming it up will often do the trick (ie. like your remote control for the TV).



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A possible fix for a Mac that won't power up
Authored by: vogunaescht on Apr 12, '05 04:07:52PM

I hope you don't mean warming up the battery. You don't want to warm up a lithium ion battery. Just google what could happen if you do that.



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A possible fix for a Mac that won't power up
Authored by: johnsawyercjs on Apr 14, '05 06:51:45AM

Actually, you want to measure the battery's voltage and its current--lithium batteries (at least the 3.6 volt, 1/2 AA batteries used to power Mac clock/RAM chips) will maintain their rated voltage even after they've practically drained away, but their current level will tell the true story; they won't measure substantially less than their rated voltage until some time after they're no longer useful. What's happened is the battery's chemicals have changed state, to the point where the battery is basically a big resistor and so they can't deliver enough current, though the voltage deceptively still looks OK. Unfortunately, many cheap digital meters don't have a current measuring scale.



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A possible fix for a Mac that won't power up
Authored by: applemandesign on Apr 11, '05 05:27:06PM

i do the same thing, w/o removing the battery. i unplug the pwr cord and click the start button to discharge the pwr supply.



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A possible fix for a Mac that won't power up
Authored by: mundie1010 on Apr 11, '05 06:52:40PM

Now you tell me! I took my dead MDD to the Genius Bar and the genius told me the odds were 99% that it was the logic board! I junked the machine! My symptoms were exactly what you described! Aaargh!



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A possible fix for a Mac that won't power up
Authored by: Detrius on Apr 11, '05 07:37:37PM

The geniuses really aren't.

This was a simple PMU issue. There's no reason to waste your time with pulling the battery out. Just push the button on the logic board.

ACSA 10.3, ACTC 10.3, ACHDS 10.3, ACDT, ACPT



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A possible fix for a Mac that won't power up
Authored by: zzzzz on Apr 14, '05 11:49:31PM

Resetting the CUDA, PMU or SMU for power related issues is such a basic step that I find it hard to believe that ACHDS, ACDT and ACPT certified techs (which is what Geniuses are) would not have tried that.

There probably was a logic board issue after all.



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A possible fix for a Mac that won't power up
Authored by: mundie1010 on Apr 24, '05 01:22:52PM

I found it hard to believe myself, but it's what happened. I subsequently managed to retrieve the machine and reset the PMU - now it works fine. There was nothing wrong with the logic board.



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A possible fix for a Mac that won't power up
Authored by: timhaigh on Apr 11, '05 08:12:33PM

Resetting the Power Manager for a none starting Mac is a standard procedure and is fully documented on apple knowledgebase. I not sure why it appears as a hint on this in 2005. When Mac users have been using the technique for years.

What is important to know is that you must neve reset the PMU button twice in a row. You must leave at least 10 to 15 seconds if you think you need to press it again. If you do press the button twice you can crash the PMU which would cause the batttery which normally last for years to expire in 3 days.



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A possible fix for a Mac that won't power up
Authored by: mike666 on Apr 11, '05 11:05:48PM

As well as keep your machine from ever booting again without replacing the logic board...

robg, PLEASE, post the instructions for a proper PMU reset procedure for desktop machines in the displayed text of any hints that get close to this subject. They are:
1. Unlpug the power cord.
2. Using a non-metalic tool (your finger, if it'll reach) push the PMU reset button (location varies by machine) ONCE and for no more than one second.
3. Wait 15-60 seconds.
4. Plug the power cord back in and hit the power button.

Note that a bad logic board, processor or stick of RAM can cause the same symptoms described by the original poster so a PMU reset is no guarantee.

"I'm never quite so stupid as when I'm being smart." -Schultz



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A possible fix for a Mac that won't power up
Authored by: timhaigh on Apr 12, '05 07:16:01AM

I don't know where the myth came from that suggests if you crash your PMU you need to replace your logic board but it's not true.

The most you can do crashing PMU is to expire the battery.

For those that want the official procedure for resetting the PMU here it is.

Resetting the PMU on the Logic Board
The PMU (Power Management Unit) is a microcontroller chip that controls all power
functions for this computer. The PMU is a computer within a computer. Its function 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.
Important:
Be very careful when handling the logic board. The PMU is very sensitive and
touching the circuitry on the logic board can cause the PMU to crash. If the PMU crashes
and is not reset, the battery life goes from about five years to about two days.
Note:
For the location of the PMU reset button, see "Logic Board Diagram" in the Views
chapter.
Many system problems can be resolved by resetting the PMU chip. When you have a
computer that fails to power up, follow this procedure before replacing any modules:
1. Disconnect the power cord and check the battery in the battery holder. The battery
should read 3.3 to 3.7 volts. If the battery is bad, replace it, wait ten seconds, and then
proceed to step 2. If the battery is good, go directly to step 2.
2. Press the PMU reset button once and then proceed to step 3. Do not press the PMU
reset button a second time because it could crash the PMU chip.
3. Wait ten seconds before connecting the power cord and powering on the computer. If
the computer does not power on, there is something else wrong with it; refer to the
"System" section of "Symptom Charts" in this chapter.
Note:
The above procedure resets the computer's PRAM. After resetting the PMU, be
sure to reset the time, date, and other system parameter settings.



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A possible fix for a Mac that won't power up
Authored by: mike666 on Apr 13, '05 12:47:06PM

I have had a number of clients with un-revivable logic boards who've told me that before bringing their machines in for service, someone they knew told them to either hit the PMU reset button several times in a row or even to hold it down for thirty seconds or more. Granted, this is just a correlation and not a proven cause and effect - more likely these folks may have just had an ESD incident while they were dinking around inside their machines or the MLBs had already failed in some other way - but why take chances? If a little fear causes people to be conservative and extra careful when messing around with a part that's US$300-500 to replace, that's less harmful misinformation than the many and varied PMU reset procedures that get propagated here and other places on the web. BTW, thanks for posting the official procedure.

(Note: Apple appears to be dispensing with the PMU - the newest G5s have a SMU (System Management Unit) which handles most of the same tasks but does not have a reset button. It's reset by simply unplugging the power cord for 15 seconds. I would hazard a guess that Apple may be tired of all the warranty logic board replacements that they've done because the user did an improper PMU reset...)



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A possible fix for a Mac that won't power up
Authored by: Riker29 on Apr 12, '05 10:53:08AM

PMU reset and/or battery removal can fix many problems.

Here is another hint:

On some Macs (like the G5 iMacs) actual REMOVAL of the battery can be difficult. A workaround is to get a small piece of paper (something which is a bit stiffer than normal paper works best like a matchbook, index card, etc.) and just slip this under the top battery contact. This effectively disconnects the battery.

Wait a good 10-15 minutes, then remove the paper, and start up.



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A possible fix for a Mac that won't power up
Authored by: foilpan on Apr 12, '05 04:19:58PM

this is a known issue with the G4 MDD models. if you browse through apple's discussion forums, you'll find plenty of evidence of this.

i support a newspaper's Macs and have had this problem with many of the MDD units. we purchased about 50 or 60 of them in 2002, and probably half of them have had this PMU problem at one time or another.

this is the one model where i've experienced this problem most often. most other newer or older Macs might need an occasional PMU reset, but not the MDD models.



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A(other) possible fix for a Mac that won't power up
Authored by: aMacUzur on Apr 12, '05 07:29:38PM

This is a copy of an email I sent in response to a mailing-list posting about a system that sometimes spontaneously re-boots after being shut down and sometimes won't boot when the power button is pressed (it was a MDD PowerMac). My (edited) response to the poster was:
-----
Your problems might be related to the following:

It turns out that some of the ATI Radeon graphics cards (e.g., the 9000 in our ol' DualGig MDD) can cause/exhibit these problems when using the DVI-to-VGA adapter with certain kinds of VGA cables. VGA cables have some pins that are either present/wired or not because they are used to indicate the "kind"/size of montior (VGA, XVGA, etc. ... i.e., the pixel dimensions).

I've found that using some VGA cables (i.e., wired to indicate some monitor sizes), but not others, will cause the following behavior (sorry, I've not figured which is which):

- when the VGA cable is connected and you attempt to shut the system down, the system will shutdown then immediately reboot (i.e., seemingly can't be shut down)

- when the system is powered down (e.g., by removing the A/C power cord) and then the power button is pressed (while the VGA cable is connected via the DVI-to-VGA adapter) the system will not not start up until the VGA cable is temporarily removed

One can imagine why this scenario occurs when you consider that the ATI card must (somehow) be connected to the power-on logic/signals because it also has an ADC connector (that supports powering on/off the system via an Apple monitor).

Anyway, I hope this helps someone ... sometime.

(Great resource, this Mac OS X Hints ... nice job!)



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A(other) possible fix for a Mac that won't power up
Authored by: Bobr on May 01, '05 04:17:47PM

I bought a used G4 Quicksilver at auction. It looks in great shape, no damage, cracks or signs of misuse. Anyway I have no luck in getting it to power up. The Front panel light will not stay lit, but the fan is running and the little red light on the mother board is lit. The DVD/CD drive clicks quietly twice on start up but other than that there is no activity. I replaced the battery and used the info you guys posted about the power button located on the board also, but still no luck. Any other suggestions? Thanks.



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works only one time for me
Authored by: marcoppc on Apr 13, '05 06:19:51AM

I have to to the same thing to power up my cube, the only problem is that it only works once. After turning the power off I have to redo the hole procedure to start it up again. (and everytime I have to remove the graphicscard to get to the reset button)

Any ideas what else I could do? (buying a new battery didn't work either)



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works only one time for me
Authored by: timhaigh on Apr 13, '05 09:50:24AM

The following check list is from the cube engineers manual. As you can see everything points towords replacing your logic board if yoru rule out issues with the power supply, dc-dc Board etc.

If have resetting your PMU your still getting issues and you've followed the procedure here, then I would use the hard ware test cd that came with your cube which will test your logic board. You would also get much more advice about your issue over at the disussion forum at http://cubeowner.com.


No apparent power (no sound and power LED is not lit)
1. Verify the power outlet is good.
2. Replace the power cord.
3. Reset the logic board. Refer to "Resetting the PMU on the Logic Board" in this
chapter.
4. Check for trickle voltage on the power adapter connector. Refer to "Power Adapter
Verification" in this chapter. If verification fails, replace the power adapter.
5. Disconnect external devices, including the monitor, and start up the computer.
6. Remove internal cards and start up the computer.
7. Disconnect internal hard drives from the logic board and start up the computer.
8. Reseat the DC-to-DC board in its connector.
9. Check the modem connector. If the connector has any bent pins, replace the logic
board.
10. Replace the logic board.



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