27 Feb
2008
27 Feb
'08
3:23 p.m.
>> Do you know that the fan is the original
one? Is it possible that
>> somebody has replaced the fan with a lower airflow one in a misguided
>> attempt to make the machine quieter?
A good idea, but I don't think this is the case. According to the technical I've not done measurements, however the fan seems
to be operating correctly,
good airflow, doesn't sound like it's dragging etc. The sound and airflow
are not noticibly different from the other two boxes.
It sounds like it's OK. What I normally do to detect a dragging fan is to
watch it when I turn the power off. If it stops very quickly, it's time
to dismantle it and clean the bearings...
According to the technical manual, the fan is supposed to be "variable speed".
It's a 12V DC fan, however it is powered via a 7905 (-5V) regulator which
has it's reference through a resistor divider which includes a thermistor.
So presumably it speeds up as the cabinet gets hot - since the thermistor is
in the power supply, which has somewhat of a separate airflow path (metal
plate between PS and boards) it may not detect the "hot spot" forming at
in the other airflow path.
I'll have to do some measurements. I could try hard-wiring the fan to full
power, however this thing *should* work as it is designed, and the fan supply
True. On the other hand, if making the fan run at maximum speed all the
time keeps the machine running, it's worth doing that mod (IMHO) to save
the problem of replacing the CPU or FPU chips.
-tony