Fans in overdrive but fails to boot I have an Apple Xserve Intel Xserve3,1 with dual quad core cpu and 48gb ram.

Today the system fans started going into hyperdrive (i.e. very fast and very high pitched) and was unresponsive to keyboard input and had no display.

So I stripped the system down, blew out the dust from the system, including the channel vents beside the drive slots and cleaned it out properly.

However, upon restart the same issue occurred with the fans and the machine did not boot, although a huge amount of air is now expelled from the system whilst it is running.

Tried various things to get a fix:

This is sequence A:::


Removed power from the machine.
Held down the start button for five seconds+
Held down the system identification button for 5+ seconds.  Other help sites suggest that this should toggle the boot sequence by flashing the blue lights on the front of the machine, but none of this eventuated.
Added power to the machine, still no change in behaviour.


Removed the fan block from the machine, and retried sequence A with no luck.

Removed the CMOS battery from the machine, and retried sequence A again with no luck, and rest times between power off and CMOS battery removal, again with no luck.

Powered the machine up with the power button depressed.  At this stage something appeared to change in behaviour.  Reassembled the machine, inserting the battery and fan pack and placing it back in the rack.  At this stage the UPS decided not to power up, so using a separate power cord, booted the machine up.  All seemed to work as per a normal boot up, although I had no console the drives, cpu lights, etc, all seemed to do a normal boot and hum as per a normal system operation for a number of minutes.

After resetting the UPS and getting it to power up, turned off the Xserve using the front off/on switch for 5 seconds and shut it down.  Plugged the UPS power into the machine and the original condition returned.

Took the machine out of the rack, stripped it down again and went through the above procedures a number of times, with a non-ups power connection and was unsuccessful in achieving the same state I had attained before.

There is a switch in the middle of the motherboard (no idea on it's intended purpose but some online information tended to point me in the direction of thinking that it was a power management unit reset (PMU reset)) so I tried that whilst running, whilst unpowered, and whilst powering up for various time durations of holding it down, all to no avail.

So, in essence, it appears as if the machine thinks it is in a overheated state and I am unable to get it out that state through various reset mechanisms that I have tried.

Another point of interest is the yellow lock light next to the locking switch is half highlighted.  Turning the lock increases the illumination level of the lock light, and unlocking it returns it to the low glow level.

Can anyone provide a solution to reset this machine so that it can boot again correctly please.
The trick appears to be:


Disconnect the power cord
Wait for 10 seconds until the front lights go out.
Insert the power cord.
Wait five seconds and then press the off button.  It must be between 5-7 seconds that you must press the off button.


Resetting SMC on Mac/Xserve