Power Mac G4 MDD - Won't power up

Before spending the big bucks for a new power supply, try a fresh PRAM battery. You may also want to try taking the old PRAM battery out and see what happens when no battery is installed.

In case you're not familiar with the PRAM battery, is looks like this:

http://eshop.macsales.com/item/Newer%20Technology/BAA36VPRAM/

It's an easy do-it-yourself fix. Batteries are cheapest online. Radio Shack sores sell them as part number 23-026 but their price has jumped to between US$15 and $20.

PRAM batteries should be replaced every 3-4 years, more often if the computer is disconnected from wall power on a regular basis. Unplugging the computer every night (or using a power strip or power backup unit to cut power) can drop PRAM battery life to a matter of months.

A one-year old battery should be OK unless you have had the computer off wall power for extended periods during that time, like the examples I mentioned in my first reply. If that is the case, a new battery is worth trying. Otherwise, I think we can eliminate the battery as the problem, especially considering that the one you installed a year ago did not clear up all the problems.

An Apple tech I know had an interesting suggestion for diagnosing a bad front panel board. He said to use an original iMac USB keyboard that has a power button. He said that button on the keyboard would override the FPB and start the computer. Haven't tried it as I can't locate such an early keyboard in this area. Still, an interesting suggestion.

thanks. i am having this problem too. i will try booting without the PRAM battery

My G4 MDD is in the same boat as yours - I just leave it on since I use it often. I will cry when it stops working... I love my Mac.

It is starting to look like the MDD power supplies are reaching their end of life in bulk these days.... The price has actually gone up over the last several months online at the various retailers I have checked regularly.

I had the exact same symptoms - starting well over a year ago:

1. Clock would be wrong on cold boot.
2. Replaced PRAM battery - did not fix the problem
3. Replaced with another make of PRAM bettery (just in case the first "new" one was bad or old.
4. The problem with no booting after a shut down began.
5. Replaced with another new PRAM battery at suggestion of others on this board and a couple of other help boards.
6. Problem still ongoing.
7. Solution - don't shut down computer unless ABSOLUTELY necessary.
8. Made the mistake of shutting down when leaving town the other day.
9. Got home and tried to boot the computer this morning... single flash of power button.
10. The usual unplug- press PMU reset button, then reconnect plug and power up did not work - just causes the light to momentarily flash while pressing the power button. Subsequent presses have no effect.
11.Listened carefully when going through the whole cycle - heard a faint buzzing begin coming from power supply after the light flashes... Keeps buzzing quietly even after letting go of the power button.

None of my usual tricks will get it to boot. I fear the power supply is toast.

Prices online range from $195 for a used one, to over $300 for a "new" one.

I wouldn't even be tempted to buy a power supply - but that I have a boatload of files on the machine that, while the most important are backed up, there are many that I really would like easier access too than to have to pop FOUR drives into external cases to retrieve the data.

Hard to fork over that kind of cash - for a machine with the age of mine (and dysfunctional firewire - have to use a PCI firewire card.

But my budget is extremely limited right now... ugh... While I really like my iBook G4 (12"), It just doesn't cut the mustard for some things I still used my Power Mac for...

I've got the blues...

I have the same problem here too. I had to shut down the other day because of storms in the area. When I tried to boot up, the light flashed on and off. I realized that if I unplugged the computer, I was able to try again. It did the same thing. I unplugged it again. This time, instead of pushing and releasing the button immediately, I held it till it actually started to power up. It worked and my computer is running. I dread the thought of it not powering up soon though as I can't afford to replace it right now.

I have an mdd that has had these same intermittant symptoms for the last 3 months. I haven't done a test of the power supply with a meter yet, but it's looking like that is at least part of the problem.

What I'd like to know is if anyone has troubleshot one of these power supplies down to the component level yet. It's got to be a simple part or two, such as a bad capacitor or rectifier. For the ridiculous price of a used power supply, it seems like someone would find some kind of other solution.

The other idea I have... can a standard ATX power supply be rewired/spliced in to power an mdd? I don't really care if it doesn't fit in the case, with the amount of heat these things generate it's probably better to have the power supply outside the case anyways.

Anyone delve in this far? Are these machines really worth it? I bought this one to upgrade from a sawtooth G4 400, but so far I don't think it's going to be worth it.

It certainly is possible to ATX up an MDD:
http://www.applefritter.com/node/23451

Mine has entered the zone of WHIRRRRRR and no startup chime, and this may be my final recourse. Though I've no idea right now if it's the motherboard or the PSU or somehow the combination of them both.

What I'd like to know is if anyone has troubleshot one of these power supplies down to the component level yet

One article ( here) traces the failure to a sloppy solder joint on a board in the PS and shows the repair. The person redid the job with his own sloppy soldering and the thing worked. His had failed suddenly with a "flash/smoke/stink" event, so suspecting a bad connection was a easy leap of logic. When the PS on my son's MDD died. it did so with nary a whimper, so I doubt that an internal fault as easy to spot as a burned connection would be the culprit.

My son's power supply was a Samsung, as was the replacement I found. Mine is the same brand illustrated in the article I linked. His PS produced zero voltage on any of the pins.

I have a Powermac G4 MDD Dual 1.0GHz machine. The machine will not boot up with either an old or New PRAM Battery installed but it runs normally without a PRAM battery. Each time it restarts from a power down the clock is 1 Jan 1970 until it can get the correct time from the internet server, but this was expected. Is it OK to continue running without a PRAM Battery? I have also noticed in the last year or so that some programs become "Not Responding" and need to "Force Quit" to get them working again. Are these two problems related?

I have fixed my mdd g4 power supply, part # 614-0224.

My g4 would not power up, the power switch light would come on but no further activity would follow. I removed the supply per the apple instructions. On the bench with supply unplugged and in its assembled state, i.e. with the covers on, I connected the ps-on line to the return line at the large black connector. You probably will want to remove the cover of this connector so you can make sure which lines you are connecting. The color code is given on a label on the supply. I then put on my safety glasses, plugged in the supply and measured the output voltages. 5.0Vsb and 25.0Vsb were as specified, but all the other voltages were at zero. *I do NOT recommend attempting to debug the supply with the covers off because there are dangerous voltage levels within the supply.*

I then unplugged the supply and disassembled it. I saw a large electrolytic capacitor that appeared to be the output capacitor on the first stage converter (the rectifier). It appeared undamaged, but these capacitors have inherently poor reliability. Additionally in this application the capacitor is subject to high component stresses. The capacitor was labeled 390uF, 420V, 105 deg C and manufactured by CapXon. It has a diameter of 35mm and a height of 42mm. After noting the orientation of the capacitor, i.e. which connection was negative, I removed it. I purchased a replacement capacitor manufactured by Nichicon rated at 390uF, 450V, 105 deg C in the same case size for $7.50 at a local electronics supplier. Although common, I would not recommend a capacitor with an 85 deg C rating. Ideally one would compare the ripple current rating of the replacement and original capacitor but I did not know the rating of the original capacitor or the actual ripple current. I installed the new capacitor, making sure the negative terminal of the new capacitor went to the same point on the circuit board as that of the old capacitor. I assembled the case and plugged the supply back into the mac. It powered up without incident.

I expect the failure of this capacitor is the dominant failure mode, so you may want to invest $7.50 and see if it fixes your supply as well.

My old QuickSilver needed a new power supply a couple of years ago and now I suspect the new one may be dying. The system has been automatically restarting itself every couple of days for a while now (though I think this could be due to a dying hard drive), and yesterday it wouldn't turn on manually until I let it "rest" for a little while.

There could be thermal issues. While tending to it yesterday I vacuumed the dust out of the cooling vent holes and maybe it will run cooler and more reliably now.

RedDoggy,
Can you detail how you fixed you power supply. I am pretty good with electronics but could you specify how you found the PS-ON line and the return line. There is no color label on my supply.

I am not convinced it is the ps but want to bench test it but need to know hte color codes.

Any help you could give would be greatly appreciated.

I figured out how to test the supply. Black (ground) bridge to the Green (PS power on) lead and PS fires up just fine with correct voltages going across all leads.

When I insert back into the computer, I get the powerswitch led lighting up for about two seconds (when I hold it) and then going back out.