For factory retro-fitted fans.
3 faults in one just fitting a fan and power bleedoff

For random fan stoppage - look for
Instead of 47R 5W W/W placed in line with the fan (dangling R unsupported at
one end) , 0.047R soldered-in so 21V across the 12V fan. Surprisingly
thousands of hours of unproblematic use like that.

Even without that , for any long term excessive wear on the bearing of fan ,
the reaction force pushes the impeller towards the mounting bracket,
eventually touching it. You could see a slight trace of where one fan vane
had rubbed the bracket and rubbed the plastic of that vane, ie clear of
usual gunge.


Replace with 47R, supported, and new fan with the centre section of the
mounting bracket hacksawed out.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/