G4 MDD power button going bad?

Question

Hi all -
I'm using a g4 MDD dual 1gig machine. Has been working great for the past few months, till just now. When I power down, the computer won't restart, unless I unplug it. (what?) That's right, the computer works fine, I turn it off and the power button will not turn the computer on unless I physically unplug the machine for a split second. After that it powers right up (at least for now). Prior to unplugging, the power switch does nothing, no lights, no chimes, nothing. It's like there is no power going to the compuer at all.
Does this sound like the power button is going bad or maybe something else? A few months ago I had PRAM/ PMU issues - could they be coming back?
Any advice is much appreciated. Thanks in advance!

Answer 1

I took care of my power-up issue tonight by working on my power supply. Here is the posting I made in another thread:
Here is what I did to troubleshoot my power issue. Your power supply can be serviced and this post offers a couple thoughts and some troubleshooting suggestions. Please read it through to the end. This isn't a cure-all for all G4 Macs, but the steps I followed seem to cover a number of bases and might prove helpful to those who are really frustrated.
I've owned a Mac every year all the way back to 1987 and have never had an issue until now and I am convinced my problem may have been triggered by a power surge or brown-out, which we seem to have experienced a lot of around here lately. This post refers to the Samsung power supply with Apple Part Number 614-0224.
I have a G4 Dual 1.25 MDD I purchased in 2003. I have had a brief issue with powering up my CPU. It wouldn't power up last weekend. I unplugged the power cord, then reconnected it to the machine and it powered up. I reasoned the power cord had become loose, but then last night I couldn't get it to come up at all. Not even a click. No lights.
So I tried all the easiest possible solutions: resetting the PRAM (pulling the battery from the logic board) and resetting the PMU (Power Management Unit). The switch, by the way, is located near where the ATA drives plug in to the logic board. Neither of those two things solved my problem. The CPU would still not power up.
I checked the lithium battery voltage with a voltmeter. It was at 3.6v, so it was still good.
I then decided my issue was probably with the power supply. With the power cord disconnected from the back of the CPU, I pulled the black power connection from the logic board and performed a power supply voltage test following the pin schematic found in this thread:
http://docs.info.apple.com/article.html?artnum=58561
The +5v trickle voltage found at Pin 9 was not present. I had no other voltage readings on any of the other pins. My issue HAD to be with the power supply.
Tonight I removed the power supply by disconnecting all of the optical drives (I have two DVD burners in this unit), all of the hard drives (three) and all of the logic board connections.
I removed all of the screws from the outer casing of the power supply, including the fat screws attaching the two black fans to the unit and the one long screw in the middle and near the edge of where the two fans are. The casing came right off.
There have been a lot of questions as to whether there are fuses in these power supplies. There has to be some protection for them and I have yet to see any power supply that did not have a fuse or resettable circuit breaker. This power supply was no different...it has a 250W, 8A fuse that is easily accessible and is located on the same side as the male power socket, near the edge of the circuit board. It is hiding under a yellow shield and is right next to a plastic connector.
Bingo! My fuse was blown. Many glass fuses will show some sort of blackness and mine did, as well as being able to see the actual glob of metal where the fuse burst.
What caused a fuse to blow will be different for each machine. I believe in my case it suffered from a power surge. There were no visible signs of burns from arcing, popped capacitors, shorts or bad chips. The board was completely clean, which tells me the issue was near the power source. The fuse may also have been on the verge of popping when I unplugged and reconnected the power cord.
Everything's speculation, but replacing the fuse did the trick in my case and I saved myself time and about $150 (on average for a used PS on eBay). I picked up a second fuse to tape to the inside of the CPU, near the power supply, so I will have a backup fuse if I need it in the future. I may also have a drive that is going bad, or I may have too many drives operating off one supply. My Mac's been configured like this for about five years now. I will replace at least two drives with new, larger capacity drives. I keep my video and digital image files on separate drives, but have a third drive I can blow out. That surely will help prolong the life of my power supply.
While I had the computer apart I gave it a good vacuum and a little air can action. Dust can aid overheating and defeat the purpose of good airflow from fans.
Hope this helps.