Power Macintosh 6500/275 - variable fan speed?

[ry755]

I recently got a Power Macintosh 6500 and after playing around with it for a little bit, I could've sworn I heard the fans ramp up and down every now and then. But as far as I know, these older generations of Power Macs don't support variable fan speeds, right? The reason I'm curious about this is because if this computer in fact *doesn't* support variable fan speeds, then I'm worried that this might be a sign of a failing power supply.

 

[Powerbase]

Which fan sped up? The CPU or power supply fan? Might just be a bad fan.

 

[ry755]

I'm not quite sure honestly, it's hard to tell. I would assume the power supply fan would be the louder one since it's larger.

 

[Powerbase]

Probably needs lubricated or replaced probably. I dont believe those fans were variable.

 

[Phipli]

It can be caused by something blocking the airflow, varying voltage or a worn out fan.

I'd stick a multimeter on the 12v (a molex?) and watch it while running a disk benchmark. Does the 12v dip?

Interestingly, some older macs had variable speed fans. Some fans had built in temperature sensors. I think the IIfx fan might be variable speed?