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Level 1

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G4 MDD won't start after a power outage

My trusty G4 MDD Dual 1.25 GHz (M8570) has been a true workhorse for the past 6+ years and has performed almost flawlessly. However, I just experienced my first major problem with it, and am in search of some guidance. I’ve spent a few hours reading through the numerous topics here that I believe to be germane to my issue, and have collected lots of useful information and made copius notes, but unfortunately, I still haven’t yet found a solution. So please bear with me!

This past weekend, my neighborhood suffered an 11-hour power outage due to a windstorm. I normally keep my MDD plugged in when it’s not in use, but not turned on or in sleep mode. The power cord is connected to a decent, commercial-grade Isobar power strip with a surge-protection feature.

When I went to use the computer on Monday morning, it wouldn’t start. The MDD’s power button lights up when pressed, and goes out when I release pressure on it. My 20-inch Cinema Display’s (A1038) power button also lights up when touched, and goes out when I remove my finger.

I initially suspected that the PRAM battery might’ve gotten drained during the power outage, so I replaced it with a new one measuring 3.6 volts as part of a logic board reset. When that failed to achieve a normal start-up, I performed a PMU reset. Still nothing.

While I normally turn the computer on using the Cinema Display’s power button, I had read about problems with the MDD’s power button board, and per a suggestion found here, I attempted to start it with an almost-new Apple USB keyboard with a built-in power button (model M2452), but that didn’t work.

I’ve read a lot about power supply failures here on the G4 MDDs, and am hoping/praying that this isn’t the problem with my machine. But this raised two questions:

a) Since the Cinema Display gets its power from the MDD via a 28-volt ADC connection, can I presume that since the display’s power light illuminates when touched that the MDD’s power supply is functioning normally?

b) Does the red LED on the logic board illuminate whenever power is supplied to the computer, or only when the computer is on and running? The LED is not illuminated right now, presumably because I can’t get the machine started.

I don’t own a multi-tester, but I guess my next step would be to purchase one and start checking things, beginning with the +5V trickle charge from the power supply. I also own a G4 Sawtooth that could be cannibalized as part of a rescue operation, but I don’t believe that there are many (if any) interchangeable components between the two machines.

Any guidance would be very much appreciated.

Power Mac G4 MDD Dual 1.25 GHz, Mac OS X (10.4.11)

Posted on Dec 1, 2009 8:56 AM

39 replies

japamac

Level 7

24,400 points

Dec 10, 2009 6:12 AM in response to garp_ct

how exactly does one test the individual pins on the PSU connector without first unplugging it from the logic board?

One accomplishes this by pushing the probe down alongside the wire into the connector.
Once the probe reaches the collar of the connector pin, a reading can be made.

Alternatively, with small, sharp probes, one may pierce the insulating plastic on the wires to obtain readings.

It is important for the connector to stay plugged in to the motherboard, as continuity is needed for the PSU to respond properly (working or not).
An unplugged connector will cause the PSU to automatically cancel voltage to a number of pins.....

xarcos32

Level 1

0 points

Dec 10, 2009 9:13 AM in response to garp_ct

Brilliant. I hope it works... although reading japamacs post makes me wonder if the results you got testing the pins were related to disconnecting the logic board.

I'm trying the PMU reset today when I get home and if that doesn't work I will replace the battery.

Good luck.

garp_ct Author

Level 1

0 points

Dec 10, 2009 10:04 AM in response to japamac

One accomplishes this by pushing the probe down alongside the wire into the connector.
Once the probe reaches the collar of the connector pin, a reading can be made.

Alternatively, with small, sharp probes, one may pierce the insulating plastic on the wires to obtain readings.

Thanks very much for explaining this. I just pulled the plastic cap off of the PSU connector, and unfortunately, my multimeter’s probes are too large to reach down inside to the individual pin collars. I’ll have to check my junk drawer and see if I can jury-rig something that adequately extends the probe tips, and then perform the voltage tests again that might be an easier workaround for me than piercing the insulation on individual wires. In the meantime, the other G4 MDD is on its way to me, so if the problem with my machine turns out to be something other than the PSU, at least I’ll have a readily-available parts supply.

Dec 12, 2009 9:47 AM in response to garp_ct

I don't know if this adds much to your troubleshooting. But I've had the exact same thing occur this morning. My G4 MDD Dual 1.42 went to sleep as normal about 11:30 last night... this morning the normally pulsing power indicator on the right side of my monitor was dark. I tapped it, and there was a brief pulse of fan noise then nothing. Now, no more fan noise, just a corresponding light as my finger touches the power=on/off area of the monitor. Same result with the G4's power button. I suppose the only thing this adds to your troubleshooting is that the power-outage that occurred a few days ago for you likely wasn't the culprit. Seems these machines have some part with a Dec. '09 expiration date. :o) Bummer, but it's been a trusty machine for these last long years... never a complaint.

brittne1

Level 1

4 points

Dec 15, 2009 7:10 PM in response to garp_ct

I'm brand new here. Please be kind.:) I am experiencing the same problem stated in this forum. I tried the remedies suggested (pmu reset etal) and the problem persists. I checked the pwr supply and found good 5 and 25 Vsb outputs but the +/- 12 volts, 3 volt, and 5 volt outputs were bad. Is there a schematic available for this unit (PN 614-0224) that anyone is aware of? Or could someone advise what I should look for before or after I remove the unit?

Dec 17, 2009 2:37 PM in response to WebHarmony

This just happened to my Dual 1.42 as well. I shut the computer down for a vacation seven days ago and after returning home I can no longer boot the computer. The same symptoms as listed previously are present in mine:

-pressing the power button causes the LED to flash briefly
-holding the power button doesn't seem to keep the light on
-fans start to rev but immediately stop
-after a few attempts the power button and system stays completely dead upon pushing the power button.

No time to run the troubleshooting steps no I'm looking forward to information regarding the PSU replacement.

Message was edited by: Chris Portle

brittne1

Level 1

4 points

Dec 17, 2009 8:41 PM in response to Chris Portle

I just removed the psu from my unit. Go to the following for instructions.
http://docs.info.apple.com/article.html?artnum=26259

garp_ct Author

Level 1

0 points

Dec 22, 2009 12:35 PM in response to WebHarmony

Well, it took a little longer than expected for my ”parts machine” to arrive, but it finally got here this morning. I’ve just finished performing my very first PSU transplant procedure, and voilà I’m back in business! I’m posting from my original beloved G4 MDD right now.

A few days ago, while I was waiting for my delivery, I performed the PSU test once again, this time with the PSU connector attached to the motherboard, and oddly enough, I got the same results as before. I guess this is further evidence that PSU failure can be partial (as opposed to total) certain pins were receiving appropriate voltages, while others weren’t. I’ve already begun to think about getting yet another “parts machine” at some point in the near future, just so I can have another functioning PSU sitting on the shelf if needed.

In any event, thank you very much to all who provided insights and wisdom.

Dec 23, 2009 6:39 PM in response to garp_ct

Thanks for posting the followup, garp. And congrats on finding a solution!

Incidentally my machine eventually consented to booting up. I haven't shut it down or slept it in the past week and don't plan to. I feel like I'm driving a car whose starter worked for the very last time :-D

Dec 27, 2009 7:51 AM in response to garp_ct

My G4 MDD started randomly turning off last week and became more and more frequent. Today when I pressed the power up button it didn't light up, fan didn't turn on...nothing. After reading this thread I'm guessing my PSU is dead.

Dec 28, 2009 12:17 PM in response to Zach Cross

No question. I finally got my PSU (refurbished off EBAY with a 90 day warranty for $130) - it went from California to Denver to New Jersey and back to Denver then to me just north of Denver - Priority Mail and it only took two weeks!!

Anyway, installed and fixed. Plugged all in, hit the power button and had my desktop in place in a little over a minute. Love it.

As a side note, if anyone is having a bit of trouble with their Firewire devices not mounting on startup, and then having to unplug the power cord for 5 minutes and restart, I think it is the same 12 volt part of the PSU tht might be responsible.

Jan 5, 2010 12:07 AM in response to xarcos32

This also just happened to my MDD. I had unplugged it before going on vacation and came back to these issues already described. Do I really have to get another PSU? Why are there so many occurrences of this at the same time? Why should the PSU fail after the machine has been unplugged for a week or so?

japamac

Level 7

24,400 points

Jan 5, 2010 1:04 AM in response to powerbookworm

Hi-

Did you try a PMU reset?

Jan 5, 2010 7:35 AM in response to powerbookworm

Get a new PSU. I got a refurbished one off eBay for $139 with 90 warranty. First I tried every trick available off the internet and Apple tech. It was only the forums here who guided me to the solution.

My guess about the inability to start (boot) while still able to run has to do with a 12 volt circuit which must power some boot rom - only needed to boot not for general operation. If they would spell this out somewhere in their knowledge base it would have been helpful.

I think the reason this is all happening at once has to do with the change in power supplies in order to quiet them back some years ago. There was quite an uproar over how loud these computers where (MDD), they were horrible junk!, I had to hide mine behind a sofa with a long extension for the monitor. Anyway, two things changed that. Apple supplied a modestly priced quieter power supply fix, which got rid of the high frequency noise of the PSU fans. But I am pretty certain that the reduced velocity air cooling - needed to allow the use of quieter fans - lead directly to these failures.

The remaining, so called "vacuum cleaner" roar was caused by a stupidly specified hardening heat conducting paste between the heatsink and the main processors. The processors would run 139-145 degrees and require the large cooling fan to run at higher speed. If I had known I could have fixed this long ago. Last year, because we had moved, my computer could easily be heard in the living room and I finally had a notion about the heatsink compound. I took the unit apart, used a non-hardening grease, and now for the first time since it was brand new, it is quiet. Processor ticks over at 130 degrees even when working really hard.

Jan 5, 2010 9:10 AM in response to John Bicht

I know PSU's fail all the time, but since this MDD and my previous G5 both died after being paired with an old Apple Studio Display (22 inch) for several months, is it at all possible that this display is somehow faulty or too taxing on these PSU's? Any reports of things like that? Just want to know before I invest time and money into pairing another working machine with this monitor.

G4 MDD won't start after a power outage