I removed the fan from the case and tested it and it runs. It is a 5VDC
0.50W fan and it ran with just 3V, so I would assume it is ok. I am not sure
how I would test the voltage going to the fan unless I would connect
everything back up without actually assembling the laptop. If there is a bad
circut, is it safe to assume that the m/b is the problem?
Yes, you'd need to connect at least enough that it receives
power. Assuming that the fan was supposed to run all the time,
you really don't need to reassembe to the point that laptop
"works" to run an OS or anything like that, merely being able to
have battery or power adapter connected, push the button, see
what happens. Even a separate video card, memory, keyboard, etc,
would not need connected. Again, this assumes fan always ran
immediately at power-on of system. If that's not the case,
recrease minimal environemt needed such that fan was expected to
run, then use a multimeter to take reading. If plug is then
inaccessible you might need a duplicate fan header plug to plug
in a couple of leads (wires) that extend out of 'book casing far
enough to take voltage reading.
I have no idea where fan connects on your particular notebook but
yes, it is usually a motherboard failure. There could be a
visable sign of it, like a dicolored/burnt trace, or something
like an inline fuse which could be checked for continuity. A
motherboard fan circuit would possibly be easier to repair than
many other motherboard problems but certainly it might require
some skill to do it. An alternative would be to find the 5V
output on the power board (circuit connected to AC adapter input
jack) and wire fan direct to that, but of course it's going to
always run at full speed, if it had been controlled to run at
variable speed that feature would be lost. Such a modification
is not something I can provide more detail on since i don't have
the laptop in front of me, if you feel you know how to do it
you're already in a better position to figure out where/how.