The PS3 Fan Test can damages your system, the fans speeding up is a fail safe trying to get the bottled up heat out of the system, this can burn your CPU and GPU, this is confirmed by Sony
That was .....---> http://www.n4g.com/ps3/News-134635.aspx here
But that sounds like it was aimed at the 60 gig i meen its obviusly stupid to overheat your machine .
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if it wasnt safe then why would it be possible?
ive done it once
As I'm aware the 'fan test' is performed by holding the eject button on the 40Gb model. I can't possibly see how this would cause any harm what-so-ever. Coming from an IT background, virtually all servers power up their fans to their full speed when first turned on primarily as a diagnostic function. Fan speeds are variable (as with the PS3) to provide more cooling when required, and to reduce noise, energy and wear when not required. The fan test allows the system to ensure that they fans are all functioning correctly and are able to obtain a specified maximum rpm range when at full power.
I'm assuming that the PS3 fan test is the same and would be a tool used when servicing or troubleshooting possible overheating issues. Somewhere behind the scenes the fan speed indicator will be reporting to the system the maximum fan rpm achieved during the test.
This test would place absolutely no strain on the PSU or GPU and the only possibly way I can see it damaging your system is if you did it enough times to eventually wear out the bearings in the fans.
Obviously achiving the full fan speed by blocking all the vents is a completely retarded way of making the fans spin faster as they are responding to a programmed temperature event and trying to do their job as opposed to just being tested.
I wouldn't recomend doing a Fan-Test.
I have heard that this is what Sony do when and if you send your unit in for repair, which would make sense.
And also there is no mention of it in any of the manuals or anything, I wont be doing the Fan-Test.
Just get the hoover pipe and run it along the vents, thats the best way.