iMac G5 "invalid memory access"/"decrementer exception"

Discussion in 'iMac' started by habejr1, Apr 7, 2011.

  1. habejr1 macrumors newbie

    Apr 7, 2011
    I'm not too good with this stuff, so PLEASE bear with me throught this long and hopefully descriptive enough situation.

    Yesterday night: iMac G5 was operating perfectly. I did not shut it down before bed.

    30 minutes ago: It appeared to be asleep (power light was on) so I clicked and pressed keys, but nothing happened. The screen remained black. I restarted with the button on the iMac.

    It chimed. Then I heard what originally sounded like the cd drive trying to engage. Then a bit of screen flickering before an open firmware message appeared saying something about not holding down keys during startup. I checked the keyboard, and nothing was on it. I air-dusted the keyboard to be sure, and attempted another restart.

    Chimed. Tried to engage cd drive? This time it was another firmware message that said something like "Invalid memory access" followed by several numbers. I thought maybe there was a blank cd in the drive and the computer was trying to boot from it. I checked. No cd. it said to type mac-boot to continue - so I did. Then, it ran through the same flickering (which had now slowed down enough to notice it contained the tiny MacOS folder icon alternating between a happy face and question mark). Then a gray kernal panic thing popped up over everything.

    But wait. There's more. I shut down with the button. I thought maybe unplugging it for a minute could do the trick. I tried. When I started it up again, I was greeted by a new open firmware screen. This time it referenced a "decrementer exception" of course followed by a ton of numbers. I typed mac-boot to continue. Then I was taken to the alternating folder icons again - this time back and forth and back and forth over and over until I shut it down.

    This is now the same result I get each time I perform the last step. The computer is obviously a little old - but it was my first Mac (excluding the performa) and I really don't want to lose it. But, I really can't afford to drop 300 bucks on fixing it.

    Any and all advice would be ABSOLUTELY INCREDIBLE! I thank anyone who took the time to read this deeply.

  2. CubeHacker macrumors 65816


    Apr 22, 2003
    Sounds like either the RAM has gone bad, or more likely, you are suffering from the common iMac G5 capacitor issue. I would search google for 'iMac G5 capacitor' and you should find several websites describing the problem, along with images of what to look for.
  3. habejr1 thread starter macrumors newbie

    Apr 7, 2011
    Thanks! I popped open the back and removed/dusted/put back the RAM. Same result. Then I looked into the capacitor issue (which sounded familiar). Turns out, 3 or 4 are broken (and a few more are bulging). I'm pretty sure they fixed the issue before and that it wasn't considered an Apple Care service as it was a common problem. I'm taking it in tomorrow to see if they'll give me the same treatment. If not, perhaps I'll buy a kit. Fingers crossed that capacitors are the only problem.

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