Mac G4 Suddenly Power Off (SPO)
- Suddenly Shut Down

The problem are like this:

"After 20 minutes to an hour of running, the machine will completely power itself off (suddenly, i.e., no Power Off). This is pretty annoying to say the least... The problem can occur in the Finder, in Terminal, in Safari, ... I think I may be experiencing an over-heating problem (as mentioned in many other posts here). I'm not sure -- I am looking for tips for diagnosing and then tips for fixing (if possible). The hardware stats: PowerMac G4, Dual 800 MHz G4s 512MB of RAM ATI Radeon with 64mb of VRAM (ATY,R200) OS: MacOS X 10.3.4 Steps that I have already taken: - I have installed a second fan (PCI slot fan) to provide extra air movement (for cooling) -- I think this has extended the time before SPOS. - I have installed ThermographX -- but it doesn't run on my machine because apparently the G4s in it have temperature sensors disabled (or so it says) Any specific help much appreciated."

"I am having the same problems!!! g4 shuts down without warning. It has done this from the day I got it. apple not helping much. I have Quick silver with apple display. I just took it into a shop and they replaced the video card fan. But 1 hour after getting it home it Power Off again. It has done this even running off a cd. please need advice.."

from

This is my story: The computer is an early (1999?) Macintosh G4 model -code name: sawtooth, 450 Mhz, 512 Mbyte RAM and AGP graphic card. Running under OS 9.2.2 and 10.1.5. I had own this computer (spring 2004) a couple off month when I first started notice the Suddenly Power Off -SPO (Suddenly Power Off). My first action was to do nothing, but after 2-3 SPO I check the battery voltage. (I have worked in the electronic industry with quality control and designing electronic test equipment). It measured 3.7 Volt. The battery should read 3.3 V to 3.7 V. Then I reset the computer PRAM according to Apples instructions. Worked just fine -for at couple off days. My next try: reset PMU (Power Manage Unit) on the logic board: I disconnected the AC power cord, removed the battery, push the small switch on the logic board, waited 10 hours, reinstalled the battery, connected the AC cord, pushed the start button -and the computer worked just fine -for at couple off hours- then the SPO happens again.   [Apples instructions for resetting PMU ] I normally use OS 10, but I tryed OS 9 to see if SPO was an error in OS 10. After 20 min I know that SPO happens in both OS10 and OS9. I try to run with the case open. Yes, that is a heat problem... But, no -SPO happens again. Connectors are sometimes a problem. I unplug and plug in connectors on the logik board several times. Did not help. Use contact spray, but still -SPO again. My next step was to return to my XP. And I start to think that Bill was not soo bad after all...      - - - A month later, on a rainy summerday I pushed the start button. My computer start to work and no SPO. But after 7-8 hours it happens again. I notice that, when I start the computer it was shorter and shorter time to SPO. Multiple restarts ended up with 1-2 seconds to SPO. End of that try. A week later i start the computer again. It worked 15 min. The same pattern -shorter and shorter time to SPO after restart. (You can see it clearly if you open the case, there is a LED on the logic board.) But when it worked I notice that it was no way I can put the computer in "sleep mode". I talked with an Apple Service Partner and they told me that it was the Power Supply (80% probability). The other possibilities was the Logic Board or the CPU. The Power Supply is expensive (I was thinking of running only the Power Supply outside the computer in a test setup or bay an PC-ATX PS and modified it according to this link). But I did´t. Capacitors are a common failure component in Power Supply's, so I open my computer case and toke out and opened the Power Supply. WARNING -hazardous voltage inside the computer, especially the Power Supply. Don´t do this if you don´t know what you are doing. It was not easy to replace component. Heavy components are fixed with glue. With computer case open I disconnected all disks, DVD and removed SCSI-board, video card, USB to mouse/keyboard etc. I was running only the Power Supply and the Logic card. Still -It was not possible to start -SPO after seconds. Then I inspected soldiering on the Power Supply PC-board. It looked like the soldering was not good -so I resolder the coils, capacitors and other heavy components. (REM: Due to the construction off switched power supply's -like this one- vibration at high (mechanical) frequency can make solder bonding collapse after a period off time). I search the Internet and found a firmware upgrade from APPLE firmware 4.2.8.       apple Download page -all languages firmware 4.2.8. EN "fyrskeppsvagen -local file- English version" firmware 4.2.8. SV "fyrskeppsvagen -local file - Swedish version" This upgrade is done in system 9. Then I installed the firmware. I was unable to finish the installation off the firmware. Then I reinstall 9.2.1 and then upgraded to 9.2.2 and installed the firmware. Still with the PS open I turn off the computer and resolder the Power Supply again. THEN I start my G4 and i don´t think it was true, but it worked OK. No SPO!!! And I can set the computer i sleep mode. It has going OK now for two month. conclusion: never give up!    2004-09-13 I spend more than 40 hours trying to locate the error. And 40 more hours thinking about what was wrong with my Mac G4 -software or hardware error? In my state off mind I broke the golden rule off fault detection: Never make more than one correction at time. I can´t tell you what the error was ... But i think it had to do with the firmware or OS9. I personally think that the Power Supply was OK all the time -but I cant´t be sure about that. Electrolytic capacitors have a ability to "repair themselves" during power off state. And when voltage are applied they are stressed to fail. So it´s a pattern for the shorter time to SPO after a SPO and that it run for a longer time after days off power off. Well -that´s my story, hope someone get some hint about what to do. Good luck! Håkan Addendum : The final solution!     2004-12-15 After a couple off months, the SPO started again. The Power Supply for my computer: G4 AGP (code name: Sawtooth), have the same output voltage as a standard PC ATX Power Supply. I decided to bay a 380W high performance Power Supply (cost < 100 $) and made some small modifications to make it fit to Apples demand. It was a little tricky to get it in position but I did.                                       Conclusion The SPO (in my computer) was caused by a -not so good- Power Supply.