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12" Powerbook G4 - fan won't turn off?

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Messing with one of my Powerbook G4 12" 1.33ghz laptops and the fan will not turn off. The unit isn't running hot or anything, but the second you turn it on the fan is revving and won't quit (does turn off if you shut the lid for sleep mode).


Any ideas?



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Yes, I have observed and recorded this failure in predecessor model. I do not know how many temperature sensors can be found in this logic board, but I know that at least one (in or near CPU) is working, and so is tachometer. Apple Hardware Test finds no problem. I inserted a twist-tie (short length of insulated wire, usually used to close plastic food bags) through vent to jam fan. Edited by butterburger
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...why would you jam the fan?

…Must I answer?

Why do you ask?


Having stopped the fan, I can use this PowerBook as intended: as a PC. A side benefit is reduced ingress of dust. (I do not have a server closet with filtered air, in which to operate a WindTunnelBook 12-inch.)

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  • 2 weeks later...

I dunno, might be interesting to see how long it lasts with a jammed fan.

Honestly like most Silicon, once the Thermal Junction Maximum is reached the chip just shuts off. Pretty much every modern CPU after the Athlon era (~2003) have a built in shut down at around 114*C. You can pretty much just take the heat sink right off under load, it will first throttle down to some super low speed (Usually the lowest in the clock table ex. 400-800Mhz) then if that's not enough it will just force shut down. Personally I'd doubt you'd actually damage anything until you get into the 150*C range. Realistically, the thermal shutdown temperature is the point at which the manufacturer acknowledges that their chips would start to see a degradation from life expectancy. Modern good binned CPU's probably have a reliable life span of around that of a human anyways (Assuming no environmental influence), especially considering the more reliable fabrication. I mean we've still got Commodores from the 80's running the AC systems in some older academic institutions that more than likely haven't seen momentary down time more than fingers on your hand.

Edited by asaggynoodle
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  • 4 months later...

Yesterday, my PBG4 malfunctioned. It was playing CD DIGITAL AUDIO (all built-in hardware: drive, DAC, amp-speakers), when it suddenly started emitting a loud noise. At first I would have described it as gunfire popping. It was loud and continuous. Desired CD audio stopped sounding, it was "replaced" with this loud noise, I did not try muting or changing volume.


Whole machine seemed to still be behaving (aside from the noise), drive was still spinning CD, trackpad and keyboard worked, OS did not hang-stall-freeze, I opened Activity Monitor (or whatever that .app was called) and found nothing unusual. I know OS and HDD were behaving because WhateverMonitor.app was not cached in memory. I chose to eject CD and actioned Shut Down.


I disconnected power, turned over, felt all around. PowerBook was mildly warm. I highly doubt it was overheating then. I removed twist-tie, reconnected power, turned on. Pop-gun noise still there, no POST "bong", Mac OS X started in safe mode. I checked System Profiler diagnostics category, it said POST passed. I actioned Restart.


Now Mac is at point of no return. It makes pop-gun noise lasting only two or three seconds (around when POST "bong" would sound?), then quiet (aside from fan, which is as loud as a vacuum cleaner). Display and backlight stay off. I hold power button to power off, then power on again, same symptoms. I power on and depress keys to reset PRAM, this seems to be doing something: after an appropriate while (about as long as PRAM reset would normally be) I hear noise again. I keep keys depressed: repeat wait time to noise, then repeat. So maybe this unpleasant noise is instead of POST sound.


Does PowerBook G4 have a POST fail sound?


I close PowerBook and put it away, then search WWW for PowerBook gunning noise, PowerBook popping noise, find nothing relevant. Then I try to think of other words to describe it, think of it sounds a lot like engine braking, so I search some more, find nothing relevant. I can record this sound if anybody is interested, but I tell you, it sounds just like truck-tractor engine brake (or some call it "jake brake").


I did find a case of different malfunctioned PowerBook noise: game show buzzer (stupidtube link).

Edited by butterburger
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