iMac Goes Into Sleep Mode If Processor Set Above Reduced Speed

Discussion in 'iMac' started by Mr. Mark, Jul 3, 2010.

  1. Mr. Mark macrumors newbie

    Jul 3, 2010
    I have a pre-Intel iMac that I bought in 2005. 160G HD, of which I'm only using 21G, so lots of free space.

    I have maxed out my RAM at 2.5 GB DDR2 SDRAM (Speed: PC2-4200U-444), which my system profiler says is "OK."

    Other info:
    Machine Name: iMac G5
    Machine Model: PowerMac12,1
    CPU Type: PowerPC G5 (3.0)
    Number Of CPUs: 1
    CPU Speed: 1.9 GHz
    L2 Cache (per CPU): 512 KB
    Memory: 2.5 GB
    Bus Speed: 633 MHz
    Boot ROM Version: 5.2.6f1

    My Mac still runs pretty well. However, I can only run the machine by setting the Processor Performance speed to "reduced" in the System Preferences. Setting it to "Automatic" or "Highest" sees an incredible increase in speed, but within a minute, the machine goes into sleep mode or shuts down entirely.

    I run Onyx on at least a weekly basis to reset permissions and run maintenance scripts. I zap the PRAM on occasion. I don't have many widgets and never use Dashboard. I've checked the Activity Monitor and don't see anything maxing out my CPU (of course, I can't do this at the higher speeds as the computer shuts down, as I mentioned above). I keep the machine well-ventilated and free of dust as much as is possible.

    In short, I've done all of the suggested 55 steps to speed up one's iMac, I have a machine with little on it with tons of HD space available, I am current on software updates from Mac, I keep a super-lean desktop and have done just about everything one can think of to get more speed out of one's machine. Yet, I can't run the CPU at anything above reduced or my machine shuts down. Worse, I know that my machine could be running much, much faster if I could run it at automatic or highest speed, because I've seen it happen for those fleeting seconds before the machine shuts itself down.

    BTW - I'm pretty sure that I used to run the machine with the processor speed set at auto, but I set it to reduced a few years ago when this shut down problem started. I maxed out the RAM after that and hoped it would fix the problem, but it didn't. I AM getting much faster performance in reduced setting with the added RAM, but it still won't work above reduced.

    Any ideas on what could be wrong? I'm thinking that perhaps my machine is just too old and can't process 2010 info with 2005 guts.

    Your suggestions will be greatly appreciated.
  2. spinnerlys Guest


    Sep 7, 2008
    forlod bygningen
    Have you taken a look at System Preferences > Energy Saver? As far as I remember from my iBook days, one could store "profiles" for different energy settings, so that while I use the battery and less performance, the iBook would go to sleep after five minutes of inactivity. If I use the iBook via AC, the computer was set to sleep after fifteen minutes. Maybe it is the sae for you here.

    Btw, what Mac OS X version do you use?
  3. crazzyeddie macrumors 68030


    Dec 7, 2002
    Florida, USA
    This sounds like the power supply or another power issue. Most of the G5 iMacs had really crappy power supplies and capacitors on the motherboard.

    When you kick it into "Higher" its probably increasing the power draw of the CPU to the point where the capacitors can't handle it.

    I've seen many G5 iMacs that exhibit this behavior right at the login screen or after less than 5 minutes of running, so you're probably lucky the machine still works reliably otherwise.
  4. Mr. Mark thread starter macrumors newbie

    Jul 3, 2010
    I'm using OS 10.4.11

    As far as Energy Saver, I have "put the computer to sleep" set at "Never," "put the display to sleep when the computer is inactive" at "2 hrs," and have NOT checked the "put hard discs to sleep when possible" box.

    Under "Options," I have checked only "Restart automatically after power failure" and, of course, have the Processor Performance set at reduced.
  5. Mr. Mark thread starter macrumors newbie

    Jul 3, 2010
    Could be. I'd imagine that's not worth getting fixed on such an old machine.

    On edit: I see that a place in Wisconsin fixes this capacitor problem for a flat rate of $200 (they admit the pats cost nothing - its the labor, which takes about 4hours as they replace all of the caps in the machine, not just any that are bulging). They also mention the power supply issues. Also, I see that this capacitor problem with iMacs of my vintage is well documented on the internet, so I'm going to assume that the caps are the problem.

    It would be worth it to get this fixed if it cost only $200. That's a lot cheaper than buying a brand new computer.
  6. Mr. Mark thread starter macrumors newbie

    Jul 3, 2010
    Agreed. I'd take it to a repair shop but I have the feeling that the cost of installing better capacitors would be out of whack with the age of the machine.

    And I can't even put the machine into higher mode because it will be stuck there when the machine shuts down. Trying to restart at that point is an adventure - seeing if the machine will stay on long enough to put it back into "reduced" mode.
  7. crazzyeddie macrumors 68030


    Dec 7, 2002
    Florida, USA
    I would save that $200 toward a new machine. Even a Mac mini would be so significantly faster than your current machine...
  8. Mr. Mark thread starter macrumors newbie

    Jul 3, 2010
    Now that you mention power supplies, it could be that. For the past few weeks, the power button on the back of the iMac has been iffy. Usually, it turns on with a single push, but sometimes, I have to push it a number of times, like locating a "sweet spot" for the machine to turn on.

    Also, I typically run an external fan across the back of the machine to keep it cool. it works, but I have to be extra diligent about cleaning dust from the iMac and the fan.

    Maybe it's the power supply rather than the caps. Maybe it's both!
  9. Mr. Mark thread starter macrumors newbie

    Jul 3, 2010
    I've been thinking about it. I'd probably opt for a laptop at this point.

    My kids just got those Dell Inspirion laptops which run Windows 7, use Pentium processors and cost under $500. Those machines run great, but they're not Macs. Of course, they're cheaper to replace when the kids spill a soda on them/drop them from a second-story building/let a friend use them/have them stolen from school/etc.

    Me, I'll stay with my Mac. Maybe get a laptop and just use this one as a back-up until it explodes.
  10. Mr. Mark thread starter macrumors newbie

    Jul 3, 2010
    Thanks for the suggestions. I've got to leave the forum now.
  11. Sun Baked macrumors G5

    Sun Baked

    May 19, 2002
    Either the power supply or you are getting a bunch of "Thermal Runaway Detected: System Will Sleep" errors in your log.

    Some people had vents clogging up and the issue went away when the fans were removed and cleaned.

    Cheap fix to try.
  12. Mr. Mark thread starter macrumors newbie

    Jul 3, 2010
    Well, I took the iMac to a local guy who has been fixing these things since the 80s. He opened the machine up and it was filled with dust and dirt, probably due to the fact that we lived in filthy Fresno for the first 3 years of the iMac's life and now live in SoCal. He said the fan that cools the CPU was caked with dirt, so he cleaned that fan up and will start on cleaning the other fan today.

    He did say that the power button was bad, the first time he'd seen that on this model iMac. That button isn't a replaceable part on its own, so his options are to create an external button that he'd wire in, or to put an entirely new back on the machine with a good button. The second option would put the cost of the entire repair up to $225, which is pretty damn cheap. The external button option would be less.

    He has been running the CPU at Automatic speed and no sleep or shut down issues.

    Hopefully, this will fix things and for not a helluva lot of cost. Then again, one never knows what he may encounter as he gets further into it.
  13. Mr. Mark thread starter macrumors newbie

    Jul 3, 2010

    I got my iMac back from the repair guy last Tuesday. As you surmised, part of the problem was with dust. The fan over the CPU was caked with dust. The internal vents along the boards were also full of dust. There was an embarrassing amount of dust in the machine, probably amassed from the time we lived in Fresno, which sports some of the dirtiest air in the country.

    There was also a bulging capacitor on the logic board and one in the power supply. In addition, the power button itself was broken.

    My guy cleaned the whole thing out, replaced the caps and did some work on the power button, which now works better than when it was new! Just a slight tap and the iMac turns on.

    The machine is running great - silent and super fast. I can run the CPU on Automatic AND Highest if I wish! The fans now come on to cool down the machine, but they never race - just like when it was new.

    Also, I've run all of my maintenance scripts thru Onyx with no problems. Ditto the clean-ups, which had been posing problems for my machine - any function that advised one to restart after running was a BIG problem in the past. My iMac would turn on and instantly turn off after shutting down after running Onyx clean-ups. Now, everything is fine.

    I think the big problem was heat build-up from dust. Everything has been cleaned out and fixed to perfection.

    I'm really happy - and it only cost me a grand total of $375. Not bad to have my iMac back to better-than-new condition.

    I'd like to give a shout out to Steve Spiegel, The Apple Doctor in Aliso Viejo, CA, who did the work on my computer and turned the job around in under two weeks. Thanks, Steve!

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