MDD power PRAM problem

[CJ_Miller]

My MDD basically works. What happens is that after I turn it off, it will not go back on again until I unplug the power cord and re-connect it. Also there is a problem with PRAM batteries. I start and the time is reset to 1904 every time... I replace the PRAM batteries, tried placing fully-chardged ones in there. They lose their charge and don't do anything.

All of this does not prevent me from using my MDD, but it is quite inconvenient. This happened with the old logic board and CPU combo I replaced, so I guess it must be the PSU? Anybody else ever have this problem, or know how to fix it?

 

[mac-man6]

Had the same problem with the unplugging and replugging it in on my MDD. The CPU and mobo were fine, I think it was the front power panel and power supply. I swapped the CPU and mobo into a different case and it's worked great since. I don't know if your PRAM battery problem is related to that but swapping cases got it working without having to unplug/plug each time I wanted to use it.

 

[phreakout]

Actually, it is a problem with the Power Management Unit (PMU) needing to be reset. The PMU is really a separate computer within itself. When it gets corrupted or out of sync, it causes problems with normal operation. One thing to remember, that is the PMU is corrupted, it will cause the PRAM battery to lose its charge within 3 days time, instead of 5-7 years.

To reset the PMU, here's what you do:

Step 1.) Unplug the power cord.

Step 2.) Locate the PMU reset button (a small, red or gray push button near the PRAM battery holder).

Step 3.) Have a known good PRAM battery on hand or currently installed in holder. If the battery is in place, temporarily take it out.

Step 4.) Press and hold the button in for 2 seconds.

Step 5.) Place the PRAM battery back into its holder.

Step 6.) Press the button one last time. DO NOT hold it in. If you hold it in, it will corrupt or crash the PMU and you'll have to start over again. Also, again, if the PMU crashes or becomes corrupted, it will cause the PRAM battery will lose its charge within 3 days time, instead of 5-7 years, as it's supposed to.

Step 7.) Plug the power cord back in and power it on. The Mac's PMU is now back in sync.

The link below is Apple's instructions for resetting the PMU. I know it is instructed for the AGP/Gigabit Ethernet model, but it works just as well for other Power Mac G4 models.

http://docs.info.apple.com/article.html?artnum=95037

Give it a try a report back with your results.

73s de Phreakout. :rambo:

 

[CJ_Miller]

Actually, it is a problem with the Power Management Unit (PMU) needing to be reset. The PMU is really a separate computer within itself. When it gets corrupted or out of sync, it causes problems with normal operation. One thing to remember, that is the PMU is corrupted, it will cause the PRAM battery to lose its charge within 3 days time, instead of 5-7 years.

Ah, yes, the old CUDA dance. I have only ever needed this on old world boxes, either because it was given to me "dead" or I had fumbled around with Open Firmware issues which were over my head. Probably came up from too many freezes and power cycling.

In my MDD G4, the PMU Reset switch is not near the battery, but rather on the corner near the IDE connectors.

THANK YOU SO MUCH for reminding me about this! I was having too many problems with this thing at the same time and started to panic.

 

[CJ_Miller]

Well, this advice worked and remedied the problem - for a while. Two weeks of disuse and the problem is back again. Nice to know a temporary fix, but I wish I knew what was causing the problem. I had the same problem with the previous logic board, maybe it is the PSU? When it finally goes into the BTX case we'll see if adapting a high-end off the shelf PSU might remedy this.

 

[beachycove]

Oh boy, I missed this when first posted.

My AGP Graphics G4 died with symptoms consistent with PMU problems about a month ago, and I was unable to revive it using Apple's instructions as referenced. However, you have detailed a different, and more detailed procedure.

It is different in that a) it refers to the battery being out first and then in after B) a first and then a second pressing of the CUDA button. Apple specifically advises pressing the CUDA button only once, and does not mention much worth knowing about the battery.

Well, Apple's instructions did not work for me, and I would dearly love to get it going again.... Are you quite certain that this revised procedure is preferable? I ask because of the "official" warnings about pressing twice (which can only mean in close proximity).

 

[CJ_Miller]

I tried each method, on different occasions. Same results.

It could be some kind of corrupt PMU ROM on the board, but I doubt it, it probably just wouldn't start at all.

Even though I just posted in another thread about MDD G4s that I have had no problems with the power supply, this seems most likely to be the issue. Also when I disconnect and reconnect the power cord, I can hear a slight electrical crackle. Maybe a problem with ground loop or static electricity? It probably could kill the logic board eventually, but I will hopefully adapt an ATX PSU before it fails...