Success!!
After a couple of hours trying all sorts of remedies I finally got two MDD G4s up and running. I also got a crash course in MDD symptoms of power failure.
Heres a quick list of steps to try. The list is created from hours and hours of reading other forums. In order of importance.
1.Check PRAM battery for correct voltage. Should be around 3.6v. For good measure I would replace even if correct voltage. WHY? Without going into long explanation. It has to do with the battery being the correct voltage but not delivering enough current. But the the battery shouldn't have to deliver that much current. Probably not but the battery is cheap and accessible at RadioShack as 1/2 AA 3.6v battery. That being said I got mine working without replacing. But i plan on replacing it now to be on the safe side. I have a feeling it just might keep the G4 running and not refuse to randomly not turn on. I've heard of people having to reset there PMU all the time. I kinda wonder if they replaced their PRAM battery.
2. PMU reset button - This should be the one of the first steps after checking the battery in resetting things and has solved many many peoples problems. Documentation says that this resets a chip. I can imagine this allows the electricity to freely flow again. I think the one misunderstood thing about the MDD G4 is its ability halt electricity in its tracks. I have a feeling this is the importance of the 5v trickle voltage or the 3.6 volt battery or both. Both those voltages would keep the electricity flowing. I truly believe that electricity can get stuck in this model of G4 and other models too. Resetting the PMU multiple times (read below for correct instructions, can't do it twice within 10-12 secs) can be beneficial for some people. Also resetting it in unique ways. i.e PRAM battery and power plug removed. Then again when plugged in. The key seems to get the electricity out of every nook and cranny of the logic board by using every method available. And I read some very unique ways of doing this. Including cleaning the complete logic board and removing all extra peripherals. Time spent with power disconnected was probably the key to those people's fixes.
Below is the correct way to reset the PMU as documented in Apple Service Manual. Please don't ask me for the service manual. I will not send it out.
Important: Be very careful when handling the logic board. The PMU is very sensitive and touching the circuitry on the logic board can cause the PMU to crash. If the PMU crashes and is not reset, the battery life goes from about five years to about two days.
Note: For the location of the PMU reset button, see “Logic Board Diagram” in the Views chapter.
Many system problems can be resolved by resetting the PMU chip. When you have a computer that fails to power up, follow this procedure before replacing any modules:
a. Disconnect the power cord and check the battery in the battery holder. The battery should read 3.3 to 3.7 volts. If the battery is bad, replace it, wait ten seconds, and then proceed to step 2. If the battery is good, go directly to step 2.
b. Press the PMU reset button once and then proceed to step 3. Do not press the PMU reset button a second time because it could crash the PMU chip.
c. Wait ten seconds before connecting the power cord and powering on the computer. If the computer does not power on, there is something else wrong with it; refer to the “System” section of “Symptom Charts” in this chapter.
Note: The above procedure resets the computer’s PRAM. After resetting the PMU, be sure to reset the time, date, and other system parameter settings.
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Troubleshooting a dead power supply? Is it really dead?
My first MDD G4 truly did have a dead power supply. I would press the power button and nothing. No fans. Nothing. On the second MDD G4 this no power no fan was the same. But after hours of resetting or maybe just finally looking for the right things I got the power light behind the button to flash when pressed. And the fans would spin for half a sec and a red light would flash for a millisecond next to the RAM. Then I would press the power button again and nothing. No light. No fan. Nothing. A combination of pulling the power plug and resetting PMU I could get the flashes to come back but still no life in the rest of the computer. I went back to the first one and tried to get some life out of it. Pulled everything. Video card. RAM. Hard drives. Finally it clicked in my head to pull out the multimeter. DUH. And check the voltage on the pins. Description of important voltages below.
There should be 25v and 5v at the following pins. I tried reading the other pins but I think the computer has to be on to get readings from them.
When dealing with electricity there is always the possibility of being shocked. Please be careful. Though I think the possibilities are low and these methods are described in the Apple service manual.
Plug the power cord into the power supply
Looking at the the power supply connector with the pinch tab on the right touch negative lead of a multimeter set to read DC power to the bottom left pin. If you care you can pull part of the plastic connector's cover off to reveal that this is a black wire for ground. Touch the positive lead to the top left which is a purple wire. You should get 5v. If you don't get 5v insure the power cord to the power supply is fully in and connected to the wall and not a power strip. Test again the pins. For the other voltage leave the negative in the same pin but change the positive to the one pin which is one down from the top right. This should read 25v. If not disconnect and retry. If either are showing no voltage or low voltage replace power supply.
After finding out I had no power on one of my power supplies I replaced it and then before installing it just plugged in the connector and pressed the power button. Nothing. I reset the PMU then got the button flash. Fan for a sec and the red light next to ram for a millisecond but no more life from the computer. It was at this time that I was reading about the power button on the ADC displays. I remember hours before that I had tried this. And nothing before. Why should it be any different. Plugged in the video card again and the ADC connector to the Apple cinema HD display and BAM I resurrected a corpse that had been dead for two years. Like I said before I had tried this earlier. I have a feeling that the many PMU resets helped to make this possible. I could actually visualize the capacitors in the Apple cinema display pulling the electricity by the hair through the tiny circuits in the logic board.
Some helpful hints to resetting the logic board
Pull everything from the board. EVERYTHING. No video card. No ram. No Pram battery. No hard drives. No ide connections. Then reset the PMU. Try even turning on the computer in this condition. Then put pieces back one by one or a couple pieces at a time. It seems many people have revived their G4s via multiple combinations of PMU resets.
Make sure to add the monitor back again later. Its very possible that it may draw power through the machine. ADC monitor or not.
A computer can and will start with no ram. Its just wont fully boot.
My computer with new/used power supply had video card and one stick of ram and ADC monitor attached when it booted up. No hard drives at all. Its interesting to note that it still will not chime. My experience with Macs tells me that this doesn't matter too much. The fact that it booted up to flashing folder speaks volumes. Possible the speaker is disconnected or broken. I also know that on laptops you can turn speaker volume down before shutdown and later startup silently. Well fans aren't that silent. But no chime nonetheless.
More Troubleshooting tips and circumstances.
Both do not chime but both boot to flashing folder. Unless POST was different back in the day it should chime even without a boot drive.
One computer needs ADC monitor plugged in to boot. And will boot with either the front button or the monitor button. Unplug the monitor and computer no longer boots. This is not the same with the other MDD G4. After first resurrection it will boot off the front button and just the power cord, no monitor. Major difference with the MDD G4 that boots with no monitor is the video card. The one that boots with no monitor has a full length video card that has some very huge looking capacitors. Its possible they hold just the right amount of electricity for a reboot with no monitor. Lets see what happens when i pull the video card. Can anyone guess.... Well that even surprised me. After being dead for about a year it now boots with no monitor and no video card. The other one needs the monitor plugged in to boot so removing the video is removing the monitor. But lets try anyways. Ok no surprise there. No booting for that one. I kinda want to find differences. Lets check PRAM battery voltages again on both machines. WHAT THE FRACK. So Mac that boots with no monitor and no video card also boots with a dead PRAM battery. And no moving dead PRAM battery to other MDD G4 does not help it. Both computers boot with no PRAM battery. But it has been reported that a bad PRAM battery has stopped MDD G4s from booting. And the fix for them was getting a new PRAM battery. So I am at a loss for what the difference could be. DVD drive is plugged in. Thats about it for the one that boots with no monitor. Both have same dual processors.
I hope this helps someone. If it helps you please LIKE my facebook page at
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Updates: So the G4 that needs the ADC monitor really needs only that monitor. It will not work with a dvi monitor or a vga monitor with a dvi adapter. What the Frack. So if I had no ADC monitor I would not be able to get this computer to work.
You all have been so very helpful!!
