DIYbanter - View Single Post

On 22 Dec 2005 13:03:07 -0800, wrote:

I have a Compaq Presario 6010 us about 2-1/2 yrs old. It has XP home
-sp2, 736 mb ram, 40 GB hd, 1.4 ghz cpu.
Several days ago It suddenly went dead, no blue screen- power was off .
It rebooted right away but crashed again in a few minutes. I smelled
something like hot phenolic material. After a little checking I found
that the power supply fan was not working. I gave it a little nudge and
it spun up. Now it quits occasionally, even if it's on in sleep mode
overnight and I have to reboot. Ordinarily I'd just get a new fan and
install it but years ago I had the same problem with a different
computer. After I'd put in 3 new fans I found that the problem was low
voltage from the power supply. Before I go and buy a Compaq power
supply or fan I'd like to determine exactly what the problem is. When
I'm using the computer I"ve noticed that the fan sometimes turns of
then on later. I moderated the fan voltage with my multimeter and found
that the voltage would drop to about 4.5v and the fan would stop. Later
the voltage would rise at about 1 v per minute until it got to 10.5 v
and the fan would restart.The fan seemed to bind a little so I squirted
in a little penetrating oil. It freed up but it still sometimes crashes
overnight. Does the power supply have some sort of heat sensor that
regulates the fan speed according to temp or is the PS going bad? The
voltage it feeds to the other hardware is satisfactory. I've never paid
any attention to this until I started having troubles.
Any ideas?
Engineman

The large hysteresis band (stops at 4.5 volts, won't restart until 10
volts) strongly suggests that your fan is toast, probably bearings.
It should vary speed smoothly and continuously as drive voltage
varies.

The fact that the voltage varies indicates that the supply does
measure temperature and adjust fan excitation accordingly. This is
very probably to meet energy saving requirements. Elex mfrs go to
great lengths to save a watt wherever they can. It may also be an
attempt to extend fan life.

Fans are mechanical devices that eventually wear out. Heat is what
kills the elex in power supplies. The cooler they run, the longer
they last. I have supplies that have run for over a decade.

If you don't mind the noise, I'd say get the biggest fan you can fit
in the available space and run it at full speed all the time. Also,
while you're in there, blow all the dust and crap out of the supply
and the puter, especially off the various heatsinks. There may be a
little fan right on the 1.4 GHz CPU. If there is, cover that when
blowing around it so you don't spin its little blades off.