iMac G4 Dead Power Supply

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Joined: Jun 5 2006
Posts: 7

Hi everyone,
My 15 inch LCD iMac G4's power supply has died. I wanted to replace it myself. Is this doable or do I need special tools and or instructions that take it out of the minors and into the major leagues?

I haven't worked on this style of Mac before, but am willing to try.

Also, what are the odds that the mother board has been effected by the failure of the power supply?

THis mac had been on 24/7 for about 5 years. I had just converted it to be an iTunes Jukebox connected to my stereo, and after a day of musical bliss it died.

Any and all help is appreciated.

Thanks, and so long for now, TOM

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iantm's picture
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Joined: Apr 2 2005
Posts: 709
information

to give better assistance - which variant of the 15" iMac G4 is this - a 700/800 mhz or 1ghz model? (the two are very different inside) Also, how did you come to the conclusion that the power supply is dead? Is it just not powering on?

Have you tried resetting the PMU (even through the button on the logic board)? Replace the PRAM battery?

If the power supply is, indeed the culprit, replacing it isn't difficult. You'll need several tools and your wits about you. You'll need a Torx 10, a torx 15, a regular phillips head screwdriver, as well as a precision phillips head screw driver. You'll need to pull the bottom cover, then the bottom case (logic board is attached to this), and the optical and hard drive assembly. You'll want to google for the iMac G4 service manual. The power supply is a two piece assembly that resides above the optical and hard drive. It's not the easiest repair, but it's easier than replacing the display arm. If you've been inside macs before (no, b&w g3, and g4 tower don't count) it's straightforward.

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- iantm
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Joined: Jun 5 2006
Posts: 7
iMac G4 Dead Power Supply

This is the 15/700/CD Drive/modem/ model. I had it to the Apple store, and they are the ones that told me it was the power supply. They also told me that they couldn't verify that the motherboard wouldn't have a problem, so they recommended not doing a repair.

I want to do the repair myself to save $$$$ (great little machine, btw).

Didn't try either of your suggestions,

>>>Have you tried resetting the PMU (even through the button on the logic board)? Replace the PRAM battery?<<<

but hope the apple people did.

The PRAM battery is most likely dead dead dead! This computer has been on 24/7 for over 5 years!

Anyother comments, suggestions are appreciated.

Thanks, and so long for now, TOM

iantm's picture
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Joined: Apr 2 2005
Posts: 709
quick fixes

Since the Apple Store is more interested in selling you a new computer than fixing the one you've already got (no offense to the Apple store staffers on here - personal observation with the guys in PGH), it's not surprising that their efforts at troubleshooting were so thorough (you've got a bad power supply, but we can't say for sure if your logic board is ok) First things first, I'd open it up (remove the metal plate on the bottom - 4 captive screws - tiny phillips), then use a torx 15 to pull the four big screws from the bottom. Once those are out, pull on the plastic, and you should now have access to your logic board. (Be extremely careful here - things can easily go wrong at this point - cables can come loose) There will be a little button on the logic board. Press it and hold down for about ten seconds or so. Plug the computer in and try to see if it fires up.

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- iantm
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As soon as I get it back I wi

As soon as I get it back I will be doing as you recommend.

I'll let you know what happens.

Thanks for the interest, and so long for now, TOM

Joined: Jun 5 2006
Posts: 7
Well, I finally got the compu

Well, I finally got the computer back and was able to open it up as you suggested. I am faily sure Apple did not crack the case because the dust inside was well preserved.

Anyway, the motherboard battery has got to be dead, so I plan on replacing that.

I looked all over the logic board for the "reset button" but so far it is eluding me. It must not look like the one in my Quicksilver G4 Desktop (I'd recognize that). Any pointers on what to look for or what it's near?

When you say plug the computer in and see if it fire up, do you mean with it in it's cracked condition, or should I reassemble it first?

Thanks in advance, and so long for now, TOM

Joined: Jun 5 2006
Posts: 7
Been workin' on iMac

Hi,
I found a service manual for my iMac G4/700 and learned that...

Warning:
Whenever the bottom housing is opened for service, you must
do two things:
1.You must clean the original thermal film from the surfaces joining the thermal
interface layer and reapply thermal paste to the thermal pipe.
2. You must tighten the four torx screws on the bottom housing to a minimum of 17
in.-lbs. If you do not have a torque driver, you will have to make sure these screws
are tightened by hand FIRMLY, BUT NOT FORCIBLY. Or, purchase the service tool
(076-0899) in order to ensure the thermal pipe is firmly mated with the top base. If the
bottom housing is not securely attached to the base in this fashion, the CPU may
overheat and become damaged. Failure to follow either of these steps could cause
the computer to overheat and damage internal components.
Refer to the topic, “Thermal Paste Application

eeun's picture
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Don't worry about the paste a

Don't worry about the paste and exact tightening of the base screws for your testing purposes. If the iMac doesn't power on you won't be heating up the CPU at all.

If you do get it working, then don't leave it on long and start looking around for paste. If you get that far, you should clean and re-paste both the CPU and where the heat pipe attaches to the iMac chassis. One of the two I restored had a ridiculous amount of paste on the chassis mount, but the original thermal pad on the CPU had dried and cracked, and the heatsink had shifted and on the cracked pad couldn't make good contact. I got it because it had thermal issues, surprinsingly ;D.

Oh, yeah...thermal paste is a compound designed to fill in the imperfections and gaps between CPU and heatsink to give better heat transfer. Arctic Silver is one I've used for years. If you can't find it or other pastes, you can cheat and use zinc daiper rash cream...at least temporarily.

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Joined: Jun 5 2006
Posts: 7
iMac G4 - Resetting the PMU Unit

Thanks for the comments on the Thermal Paste.

BTW, I finally found out about the Resetting the PMU Unit.

I wanted to follow correct procedure, but it's hard to get a feel for it. Pressing the reset through that plastic cover is like wearing a condom. Wink

Any more meaty descriptions of the process would be appreciated.

Thanks, and so long for now, TOM

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Joined: Dec 15 2004
Posts: 122
Look here

Mac PRAM, NVRAM, CUDA/PMU & Battery Tutorial
http://www.geocities.com/texas_macman/pram.html

Cheers, Tom
Mac Troubleshooting, Maintenance & Tips
http://www.geocities.com/texas_macman/MacTroubleshoot.html

Joined: Jun 5 2006
Posts: 7
Power Supply Installed - All is well!

I got my replacement power supply and installed it without too much difficulty.

Just had to be patient during the process.

Back in business.

Thanks to all who helped.

So long for now, TOM