iMac G4 Kernel Panics - Overheating?

Discussion in 'PowerPC Macs' started by pmartin, Aug 9, 2007.

  1. macrumors regular

    Apr 23, 2005

    Yesterday a friend gave me a really nice 17" iMac G4 he was planning to throw out because it was having problems. I would really like to get this working and would potentially be willing to buy parts to repair it. I have a significant amount of Apple hardware experience, but would like to get the opinions of people who may be more familiar with iMacs than myself on these forums.

    The problem is that the computer has random kernel panics. Sometimes it occurs as soon as the computer is turned on, sometimes after it has been on for a few minutes, sometimes after a few hours.

    So far, I have replaced the RAM with known good sticks, have replaced the hard drive with a tested good one from my collection (and these were both upgrades to boot!) and I have re-applied thermal paste (Arctic Silver) to all key components (CPU, ends of heatpipe, GPU) but to no avail, I still have the same problem.

    I was wondering if anybody knows what could be causing this or has any suggestions.

  2. macrumors 6502a

    Oct 29, 2004
    KP ideas

    Have you tried reading the console to give you an idea? The crash log is where I'd look.

    Does the the unit have wireless? Tried reseating it? Tried the unit without wireless?

    Not knowing the type of iMac - can you swap out the GPU for a Known good model?

    Have you tried varying the used RAM slot? (if it has two slots)

    have you tried reseating the LVDS cable / video cable?

    Have you tried booting off a known good installation of OS X eg FW drive?

    Have you tried AHD? Try loop it for a few cycles too.

    odd one...I hate this type of issue.

  3. thread starter macrumors regular

    Apr 23, 2005
    My crash log is as follows, but it doesnt give a clear indication of what's going on:

    Wed Aug 8 15:14:43 2007
    panic(cpu 0 caller 0x000A8B80): Uncorrectable machine check: pc =
    0000000000082310, msr = 0000000040009030, dsisr = 40000000, dar =
    AsyncSrc = 0000000000000000, CoreFIR = 0000000000000000
    L2FIR = 0000000000000000, BusFir = 0000000000000000

    Latest stack backtrace for cpu 0:
    0x00095564 0x00095A7C 0x00026838 0x000A8B80 0x000A7E10 0x000AB880
    Proceeding back via exception chain:
    Exception state (sv=0x385DCA00)
    PC=0x00082310; MSR=0x40009030; DAR=0x05759000; DSISR=0x40000000;
    LR=0x000821EC; R1=0x2274BA70; XCP=0x00000008 (0x200 - Machine check)
    0x000821EC 0x0007C9D0 0x002875D8 0x002A207C 0x0008A0C4 0x000611F0
    0x00063108 0x000A85DC 0x000AB880
    Exception state (sv=0x437CB280)
    PC=0x8FE155B4; MSR=0x0000D030; DAR=0x05759000; DSISR=0x40000000;
    LR=0x8FE1554C; R1=0xBFFFD2B0; XCP=0x0000000C (0x300 - Data access)

    Kernel version:
    Darwin Kernel Version 8.0.0: Sat Mar 26 14:15:22 PST 2005;

    Wed Dec 31 19:00:44 1969
    panic(cpu 0 caller 0x000D32C4): packed field size mismatch; allocated
    52 but packed 40355640 for common 000381ab vol 00000000
    Latest stack backtrace for cpu 0:
    0x00095564 0x00095A7C 0x00026838 0x000D32C4 0x002A8174
    0x000ABA30 0x026414C0
    Proceeding back via exception chain:
    Exception state (sv=0x37EA8C80)
    PC=0x9001BF00; MSR=0x0200F030; DAR=0xA0F55CB4; DSISR=0x40000000;
    LR=0x903A57F0; R1=0xBFFFC270; XCP=0x00000030 (0xC00 - System call)

    Kernel version:
    Darwin Kernel Version 8.0.0: Sat Mar 26 14:15:22 PST 2005;

    It does have Airport Extreme, I just took it out and retried - same problem.

    Not possible :(, it's an iMac G4 1GHz 17" with 1.5GB RAM (I just put in) 120GB Hard Drive (also just put in) Airport Extreme, and a SuperDrive.

    I haven't, is it possible that one of the slots could be bad?

    When I first disassembled the iMac I reseated the LVDS cable.

    I freshly reformatted the new drive I put in it.

    That would be ideal, as people claim it works well. Unfortunately, I do not have the AHD disk for this computer, is there anyway I can download it? I used Techtool Deluxe, but it didn't find any problems.

    You and me both :D! Thanks for taking the time to give me these suggestions!
  4. macrumors P6

    IJ Reilly

    Jul 16, 2002
    It sounds like you've narrowed the problem down to an intermittent fault on the motherboard, perhaps a hairline crack or a broken trace. Unfortunately, probably the only way to test that theory is to replace the motherboard.
  5. thread starter macrumors regular

    Apr 23, 2005
    I feared it was a bad logic board. Unfortunately, they seem rather hard to come by, does anyone have one to sell?
  6. macrumors 6502a

    Oct 29, 2004
    Before you go down that route - try getting an AHD for this unit. The crash log does sound to be either RAM or Main Logic Board. You're not in luck here - cos it seems like you know what you're doing, unlikely to be RAM.

    How far are you from an Apple Store? Perhaps you can go down and kindly ask for an AHD disc. If they're in a nice mood, they could burn you one...

    Alternativley, try call AppleCare and see if they might be able to help - they may charge. Try find someone with the same machine. AHD or ASD (Apple service diagnotic) would hopefully confirm / clear the idea of a screwed MLB.

    To be honest - it's not looking good. There are places that sell these service parts, but Apple won't sell them direct - they'd wanna fit it.

    Try the Known good RAM in either slot. RAM slots (one of the two CAN fail on their own) can be a bast@rd to diagnose - this is a possibility here.

  7. thread starter macrumors regular

    Apr 23, 2005
    Thanks for all of your help! I haven't talked to my Apple store yet, but I am within 20 minutes of one, and currently work right next to it so I will stop sometime this week. I did try testing the RAM slots but with no luck. Since I got this computer for free, I am not too upset, but it would be really nice to get it working. I have been looking around for a logic board but they are really hard to come by; I'll see if anything turns up though.
  8. macrumors newbie


    Apr 17, 2008

    Before You Waste Your Time AND Money, I Saw On The Web Somewhere That A Guy's iMac G4 Was Having Random Kernal Panics,The Upgraded The OS And The RAM but Kept On Crashing, But Then He Took The iMac Into His Attic Where it Was VERY Cold Took Off The Bottom Plate (Not The Whole Dome, Just The Plate) And NO CRASH!!! So It Was Just Overheating! Put A Better Cooling System And Make A Better Airflow
  9. macrumors regular


    Jun 10, 2008
    My 15" 700mhz model does this too, I may try removing the extra ram that I added...
  10. macrumors regular

    Apr 26, 2010
    Nanaimo, BC
    That would be really unfortunate if it's the logic board.

    The second error in the crash report looks like a RAM problem to me; it says something about "packed 52" but received a different value, which would lead me to suspect a problem either with the memory or with the lines of communication between CPU and RAM, which could also be the logic board sadly.

    If you want to look into the overheating issue, crack open the bottom of the unit and clean off the thermal joints between the top case and motherboard. The entire dome of the computer is a heat sink, so you should have plenty of cooling so long as the thermal paste is efficient enough (six to eight year old thermal paste is crap in this regard). Also, just check to see if the fan is running by feeling for air out the top vents. The fan run all the time on these machines.

    I perused Ebay but didn't see any logic boards, although I have seen them there on occasion. They range from $50-100 depending on the model, and you need the same one that the computer shipped with originally for it to work (so no upgrades or downgrades will work, difference in connectors and so forth). You can get these machines on Ebay for $100-200 however, so I don't know if you figure it's worth it.

    If you can get it running, they are great machines.
  11. macrumors 68040


    Dec 7, 2009
    @mike.coulter: check your RAM for sure, second is to verify HDD - maybe is going bad.
    From my experience, KPs are never caused by overheating. Mostly it's RAM and CPU/logic board/HDD problem. In general, overheating causes freezes not KP.
  12. macrumors 6502a


    Jun 29, 2008
    Don't waste your time lugging it into an Apple store. All iMac G4s are vintage or obsolete at this point, unless you're in California. Apple does not offer any support for vintage hardware.

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