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iMac G5 - fan whines hard then system hangs, must reboot

W

waywardguy

macrumors newbie
Original poster
Jan 19, 2012
5
0
Massachusetts, USA
I have an iMac G5 running 10.5.8. In a situation where, after bootup, the system works for about 5 minutes - then the mouse freezes and fan comes on full blast about 30 seconds later. All I can do is power down. Tried running TechTool Pro - baseline diagnostics check out, but when I run deeper diags (disk), the system hangs before I can complete them. I'm not a hardcore Mac/tech guy, so not sure if I have a hardware or software (O/S) issue? Or if this is a recoverable situation?

Appreciate any insights you can offer...

Thx in advance,
-Dave
 
Will do. Checked the vents (they look to be on the bottom) - wiped them, they looked pretty clear but I will get the can of air... thx. Any other ideas?
 
Took case off, no real dust inside to speak of. Blew out bottom vents, but very little came out. Are there other potential hardware or software issues that have been known to cause this issue? Runs ok for about 5-10 minutes (sometimes longer), then the mouse freezes and the fan comes on high. Nothing can be done except hard boot...

Thx for your help!
-Dave
 
waywardguy said:
Took case off, no real dust inside to speak of. Blew out bottom vents, but very little came out. Are there other potential hardware or software issues that have been known to cause this issue? Runs ok for about 5-10 minutes (sometimes longer), then the mouse freezes and the fan comes on high. Nothing can be done except hard boot...

Thx for your help!
-Dave
Click to expand...

IIRC there's a 2nd set of vents, much higher up? Been a while since I sold my G5.

It really sounds like a heat issue, and most heat issues are dust related. Here's a thought - download and install smcFanControl and see if you can get a temperature before the crash.
 
Thanks, I am beginning to agree that it is truly a sign of excessive heat. In response:

1. I tried downloading smcfancontrol, but my G5 iMac is PPC-based and when I attempt to install, it tells me it's not supported on my architecture.

2/ I have been online tonight, trying to determine what to take apart and clean. I had the back off last night - everything "appeared" clean, but I didn't have a can of air to take to it. Are there specific components I should expose, once inside, that I should blow out thoroughly?

Interestingly, I have been on for an hour plus tonight and it is still running (?)

Appreciate your ideas - thx!
-Dave
 
Could actually be a power issue, where the system is not receiving the correct voltage after a period of time. I'd check the power supply, as well as the caps on the board. IF those both check out, I'd reapply thermal grease (Arctic Silver) to the CPU. If you have any questions on during this just PM, I've done several.
 
Thanks for the replies - I will check the capacitors and the power supply. Macman, if you have any more insight w/r/t your post, I'd be glad to get it - I.e. what to do to check power supply, does 'caps on board' mean capacitors? Thermal grease application? Appreciate any info or links you can direct me to - thx!
 
waywardguy said:
Thanks for the replies - I will check the capacitors and the power supply. Macman, if you have any more insight w/r/t your post, I'd be glad to get it - I.e. what to do to check power supply, does 'caps on board' mean capacitors? Thermal grease application? Appreciate any info or links you can direct me to - thx!
Click to expand...

Sure, I'd be glad to. First pop off the back cover, Two end screws and one screw in the middle. Check all of the 25 capacitors on the logic board. Normally there will be electrolytic leaking, a brownish goo. If not, check to make sure the top of the capacitor is perfectly flat. Not bulged up at all. Next to the power supply. Remove the three long gold phillips screws the secure the power supply. Then take a spudger or screwdriver if you have to and remove the black connector on the logic board. Once you have the power supply out, first check the voltage. I'll post the pin out, but each connecter is numbered. Grab a paper clip and short out pins 15 and 16. This turns the power supply on. Of course connect the power cord, then check each connector for the proper voltage. I think this is where the problem lies. Here is the voltage for each pin:

1. +3.3 – Black
2. +3.3 – Black
3. GND – Black
4. +5v Gray/Purple
5. GND – Black
6. +5v Gray/Purple
7. GND – Black
8. PG – Blue(ignore)
9. +5.1Vsb – Purple
10. +12v – Brown
11. GND
12. +3.3 – Black
13. +12v – Brown
14. GND – Black
15. On/Off – Gray Connect these two
16. GND – Black Connect these two
17. GND – Black
18. GND – Black
19. +12v – Brown
20. +5v Gray/Purple
21. +5v Gray/Purple
22. +20v to +24v – Brown

Put the voltmeter on any of the GNDs and test each voltage. My prediction is about 75% will have the correct voltage. If you have the correct tools, I'd visually inspect the capacitors on the power supply after this. It requires a Security Torx 10. Basically a T10 with a hole in it for the pin on the nut. Check for leaking caps. I've seen it so bad it burns the enclosure. you can also check the metal under the logic board right by the power supply, I've seen burn marks there before. If EVERYTHING looks perfect, which I highly doubt, follow the iFixIt instructions to remove the logic board, and follow their directions for reapplying thermal grease/paste. I'm fairly certain you'll find the problem with either capacitors on the logic board of in the PSU. Thermal grease is a nice thing to do if you have the board apart. (Lowered my operating temp about 15-20 F!) Again, PM me with any more questions!

-Ricky

Remove Logic Board:

http://www.ifixit.com/Guide/Installing-iMac-G5-17-Inch-Model-A1058-Logic-Board/971/1

Applying thermal grease:

http://www.ifixit.com/Guide/Applying-Thermal-Paste/744/1

Oh, and directions to removing the power supply:

http://manuals.info.apple.com/en/imacg5_17inch_power_supply.pdf

Tough little bugger to get out if you've never taken one out before.

Lemme know how it goes!
 
waywardguy said:
I have an iMac G5 running 10.5.8. In a situation where, after bootup, the system works for about 5 minutes - then the mouse freezes and fan comes on full blast about 30 seconds later. All I can do is power down.
Click to expand...

I have the same exact problem. Did you ever figure out the solution?
 
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