HELP!! G4 Power Supply issue?

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HELP!! G4 Power Supply issue?

I'm having a strange issue with a DP450 Mac G4. When you press the power button it lights up but the computer itself won't power up. The machine was working fine about 2 weeks ago after I had changed out the stock DVD ROM with a 4x burner and added a SATA controller and a 400 gig drive. The machine had been off while I was out of town for turkey day. Does this sound to you like a power supply problem that could have been caused by a power surge or did I personally drive nails into this poor machines coffin?

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An idea

Did you try resetting the pram?? More-often-than-not I find that this usually remedys the problem.

If memory serves, i think it is Command-ctrl-p-r while engaging power...(or cmd-opt-p-r) wait until ther startup chime plays a second time before releasing the hotkeys.

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Thanks, no dice

It never gets to the point where there's a startup chime. The fan doesn't turn on, the drives don't power up. The only sign of life from the machine at all is that the power button lights up when you press it and then goes dark when you release it, other than that nothing. It almost seems like the power is being interrupted between the power button and the rest of the power supply. Reaching inside I noticed that the power supply is warm. That seems a little ominous to me...

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G4

You might try upluging the IDE connector from the logicboard and the power lead from the hard drive. make sure you unplug the connector from the logicboard. I bought a couple of G4s with basicly the same symptoms and it was a failed IDE connector on the logicboard

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Dang!!! Nothing...

Thanks for the suggestion; unfortunately it didn't seem to have any effect. I feel like I'm trying to shoot Godzilla with a pistol! I still have a suspicion that it's a PS issue which would be an easy and realtively inexpensive fix if Apple didn't use proprietary power supplies; I think a 400 watt atx @ Micro Center is like $15 these days as opposed to $200 for one of the Apple ones...and what if that's NOT the problem? Oy! Anyway thanks!

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Try unplugging the PS from ev

Try unplugging the PS from everything extra and see if it will start by itself.

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try holding Command+option(al

try holding Command+option(alt)+p+r. wait for it to chime about 3 times if it does.

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G4

I have a known to be good PS out of a B&W G3 400MHz machine. It looks to be the same a the PS in my G4 450. The only differance I could see was the output rating was 126 watts verses 100 watts on the G3 PS.

Does anyone know if the G3 PS will Work on a G4??

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sure

not all the watts are driven into the computer. That is just the maximum it will supply under the load. You might have actually spelled the demise when you added that stuff, by overloading the PSU. I have done this with my PC and have had similair problems. On my Second PC Supply, the fans and light would turn on for a fraction of a second, and then turn off, leaving me to have to unplug the PSU from all the electronics, and reset the board. I think the G3 PSU will do it, but let it only be a temporary solution, l'est you want to drive that into the ground too. I would just use it with nothing on the supply c'ept the Board, the HDD, the keyboard/mouse, and the display to see if it powers up. If it doesn't then it is the board.
So do a minimal setup, and slowely add the components to make sure you don't overload it at first

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Still nada;

I don't think it's a case of the PS being overloaded as the computer was powered down for quite a while and then simply didn't start. I did try removing power from all the drives with no change. We've been having some issues with the AC here and it was plugged into the bypass outlet on the UPS it was attatched to; meaning it was no better off than it would have been had it been plugged straight into the wall should a power surge happen down the pike. Anybody know if the AC/BEL power supplies have fuses in them?

The machine in question has a 126 watt power supply; A 100 or 126 watt power supply for any computer built in the last 5 years is really pathetic in any case. I don't think a 126 watt PS really provides enough power handling for day to day operation let alone any meaningful system expansion. The PCs I've built in the last 10 years or so would never have a PS of less than 300 watts (lately I've been putting 500 watt units in them). I really don't understand why Apple would adopt such a "build it to break" mentality given the limitations they have on overall computer marketshare.

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I had a similar prob

For what it's worth here's my story.

I had a Digital Audio 466, which in my eagerness to open up, instead of waiting for it to fully power down I pulled the power cord (I know it was "rash" but that's not the point of my story). After doing this my machine would not power up. The power light would stay on only as long as I held the button down and then it would die. No chime or fans.

I swapped the processor and hard drives to a machine that I know worked and they weren't the problem. After reading an Apple diagnositc PDF on G4s it looked very much like I'd killed the mother board. I never tested the PSU directly but a new/second hand machine from eBay was $200 which I transfered all my upgraded cards and processor. It seemd like an easier solution to pay the extra for a working machine than drag my broken old machine to a dealer who wanted $80 just to diagnois with no idea of cost of parts or more labor.

These docs might help you with pinning donw the problem

http://docs.info.apple.com/article.html?artnum=58561
http://docs.info.apple.com/article.html?artnum=95038
http://docs.info.apple.com/article.html?artnum=95054

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This link has a great G4 how to doc

http://www.whoopis.com/computer_repair/PowerMac_G4.pdf

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me too!

Im having the EXact same problem with my 733 digital audio, I found a page which tells how to test the power supply & tested it with a voltmeter, If I did it right it says my power supply is providing a 28v trickle to the board but the next pin I was suppossed to test was suppossed to give me 3.3v but it was dead, so I guess its the power supply. Anyone have any tips let me know, I just bid on a 22 pin power supply on ebay, I hope it works

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