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I have about six G4 MDD mac from the G4 1.25 to the dual 1.4 versions.

I have noticed that four of them have developed the problem of not turning on and the power button just giving a light when pressed ~ so not completely dead ~ however I have looked for solutions to the problem and gather that they probably suffer from power supply failure.

I would like to know if anyone has ever successfully repaired a power supply from one of these machines and if so can they identify the components that fail ? 

I have been told it's probably capacitors but don't know for sure. 

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Hi, as far as I know, the best solution is to replace the power supply with an modified PC power supply. Google "ATX power Power Max G4". A friend of mine has done this and said it was easy. I haven't had to place mine yet in my G4 quicksilver, but I will if it ever fails.

I know this helps!
BTW: as an added bonus, you could get one with SATA for newer drives (with a SATA PCI card of course!)

Jeremy:
Read this before buying anything:
Several years ago my G4 MDD 867 did the same thing and just like you I figured "old well time for a power supply".
Being busy I pulled the PRAM battery and unplugged the system and gave it a rest under my desk while I looked for an economical power supply replacement and used another G4 for the time being.
Skipping ahead nine months later, I come across an article about how touchy the energy management system in these G4s can be; upon reading this I said" no way!" And just to prove it I plugged in the unit and to my shock it booted up just fine.
Some how the Energy Management had gotten confused and refused to boot the Mac. After the G4 finally drained of all power things reset and would boot. I have also seen this happen in a Titanium G4 powerbook too
Of course I can't guarantee this is what has happened to your G4s, but if you are able to resurrect just one of those G4s this way it'd be worth the wait. Best wishes
Jake

Hi Jake,

I did have a similar result myself some time ago. I got a reply from the Apple forum suggesting many things including removing all the PCI cards because they could cause the problem. Also reseating the RAM chips. Re seating the processor and of course removing the P RAM battery and pressing the CUDA button. On a couple of occasions it has worked but some people still direct you to the power supply as the problem.

As I don't want to make a hash up of cobbling in a different power supply and chopping all the wires off to join it up. I can do board level component replacement and it would be an easier and neater solution. 

I did take the power supply out and take it apart. It looks completely clean and It has no dodgy capacitors so I will probably put it back together again and see if it works. I have had one G4 disconnected for about two weeks now and I might try it out in a couple of days time. Thanks for your comments and they do seem the most valid. 

Regards Jeremy 

Jeremy:
I also did all the same as you described and then finally removed the power supply. I'm sorry I don't remember how long the power supply was unattached from the system but my guess is that it was at least a month. Exactly how long it takes for the power to drain and the Energy Management system to reset is unknown to me.
Additionally: is there a quicker way to deplete a Macs electronics of residual power safely? These are questions I'd love for some our savvy Electronic Engineer folks to expand upon. It would definitely be a help to us and others I'm sure.
Sounds like you are making all the wise choices and I wish you success if they can be salvaged. Let us know if you do also. Thanks
-Jake

I did watch several videos on You Tube but a lot of the people are presenting themselves as experts and in fact they are ~ whats's the polite word for bullshitters ? ~ I take most of it with a pinch of salt. 

I did study electronics as I used to be in the Hi Fi Trade and did a couple of evening classes before continuing with self education before starting an HND in electronics. 

The problem is that my electronics experience started with valves and transistors and power supplies that had conventional transformers with wound cores and not modern electronic supplies which are far more critical.

Modern power supplies have become far more complex in their own right because they have to supply a multitude of voltages and currents and each is critical on the other. Also manufactures often remove identification numbers from chips to prevent copy right and design theft. In my day you used to send off for the engineers service manual with gave you a circuit diagram and test points indicating what voltages to expect at what point.

You have just remind me that I have one G4 that has been stripped and sitting by my front door for the past six months so I will drag it out and have a go wit that one.

One comment that was made was that one component inside the power supply was responsible for power management ? 

I will let you know how I get on. 

I noticed that this site is becoming a bit sparse as far as post by James & john. I gather that one of them moved and the production standards have fallen a little in terms of synchronisation of the content.

I did look for other sites that are dedicated told macs as I have so many and still use a lot of them for one thing or another. You can't beat desktop publishing on a power mac 9600 running Pagemaker on OS 8.6. I still use it for producing custom PCB overlays from circuit diagrams. These I print out on a special film on an Apple laser printer for making circuit boards for etching. Whats's great is you can also alter toner density on the printer buy talking to the printer via Apple talk. 

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