Mac Pro 1.1 (Intel 2007) rear exhaust fan always at full speed (Northbridge @ 130C!?)

[shaocaholica]

My buddy has a Macpro 1.1 (intel 2007) and his rear lower exhaust fan is going bananas. About 20sec after power on while still booting OSX, the fan revs up to full speed (~2700rpm) which is crazy for a fan its size. Its pretty ****ing loud and it stays like that. iStat Pro is reporting a northbridge temp of ~130C which is way over spec but the NB heatsink is pretty cool to the touch. We've cleared out all of the dust in the case pretty thoroughly including removing the shrouds. The next step is to clean and apply some arctic silver on both CPUs and the NB but I have no idea if that will help as the temp reading from the NB obviously wrong. We've also reset the PRAM and SMC. Oh and its running 10.5.8. We'll try a clean install of 10.6 + updates before we do the thermal compound re-application.

 

[666sheep]

Looks like NB heatsink thermal sensor failure (if so, it will be first time i ever heard about such an issue in MP). Check real heatsink temps with digital thermometer if you got one.

 

[shaocaholica]

Looks like NB heatsink thermal sensor failure (if so, it will be first time i ever heard about such an issue in MP). Check real heatsink temps with digital thermometer if you got one.

Don't have a thermometer that can read something like the NB heatsink but I can tell you its way off as I can hold my fingers on it comfortably when its reading those high temps. What about the fan? Would that be why the rear exhaust fan is running full speed?

 

[Loa]

Would that be why the rear exhaust fan is running full speed?

Well, if the computer "thinks" that northbridge is at 130C, then it will indeed blast the fan to full speed.

I can't tell you how to fix a faulty reading like this, but fans going haywire can also be a symptom of something worse. My 2008 iMac's fans suddenly began to rev at full speed for no reason, even from a cold start: 2 weeks later, the logic board, motherboard and power supply had been changed.

Try running any diagnostic tools you may have.

Good luck,

Loa

 

[666sheep]

Excuse me stupid question: did you checked this bigger heatsink, this near CPUs? There are two: smaller one under HDDs and bigger one near CPUs. I'm asking, because in my MP 2006 (with dual slot video card) is almost impossible to reach NB heatsink with finger, card's cooler is covering it almost completely.
Second thing is: where this sensor is mounted (i never removed NB heatsink in my MP)? If it's mounted direct on the heatsink and connected to logic board with cable (like CPU hs), fix should be easy (replace entire part). If it's soldered to the logic board, things are more complicated and fix will be expensive.
Maybe somebody, who removed NB heatsink in MP 1.1 (like lbodnar) could tell more about it?
Good idea is to run Hardware Test or Service Diagnostics (if you have it) like Loa mentioned.