GatewayM675PRR
Riffxyz
I have this Gateway M675 laptop It gives me a fan error when booting.I
have tried the fan assy. in another similar laptop and it works fine.
I really don't know alot about this stuff and I wonder if anyone has a
solution. I am thinking it's a motherboard problem but unsure.
Any help would be appreciated.
Thanks.
Paul
If the CPU fan has three wires, one wire carries the tachometer or RPM
signal. It pulses twice per fan revolution.
The motherboard has a chip, that measures the fan speed. The chip is the
SuperI/O, which connects to the Southbridge. The fan speed is measured,
by measuring the time period between two successive pulses on the RPM
signal wire.
A counter, counts clock pulses, to measure the time period. The counter
has limited resolution. For example, the counter might be an eight bit
counter, limited to counting from 0..255 . If it is asked to count past
255, all it can do, is record that there was an "overflow".
At 3000 RPM, perhaps the counter has 16 counts in it. At 1500RPM, the
counter has 32 counts in it. As the fan runs slower, the time measurement
process results in more counts being accumulated in the counter.
If the fan ran at 200 RPM, the counter would overflow (more than 255 counts).
The software doesn't know whether the fan has stopped spinning entirely
(zero RPM), or is spinning at 199 RPM. The counter lacks the resolution
to be able to tell the difference.
So each computer design, has a "minimum" fan speed. If the fan spins
below the minimum value, the BIOS may conclude the CPU no longer has
cooling, and shut the computer off to protect the CPU. This is
why it is important to use a fan with RPM signal on it, for cooling
the CPU, because if the RPM signal is missing or "slow", the overflow
on the fan counter will trigger an eventual shutdown.
Either the fan is spinning below the minimum speed, or the RPM wire
is broken, or the fan is no longer driving a signal on the RPM wire,
or the SuperI/O is no longer properly measuring it. The fan is
the most likely source of the problem.
On my second computer, the minimum fan speed was 1800 RPM, which is
pretty high, and easy to violate. The fan it was monitoring, didn't
really spin much faster than that. The design flaw in that case,
was the wrong prescaler value was programmed in the SuperI/O chip
by the BIOS. More recent computer designs, support lower limits
for RPM, moving from 1800 RPM down to perhaps 500 RPM or lower.
But you should first examine the fan carefully, and make sure it
really is spinning fast enough to cool the CPU.
I suppose another possibility, is the computer isn't sending any
power to the fan, so it can't spin because it has no power. That
would be a motherboard fault. And they *never* uses fuses in the
fan power path. If the fan header lacks power, a copper track
could be burned out. For "controlled" fans, a pass transistor
could be defective. And those would be motherboard faults.
You can use a multimeter, to verify the fan is getting power. But
that requires great care on the part of the operator. Shorting
the probe tips together on the multimeter, in the middle
of a measurement, can damage the motherboard for example.
For voltage measurements, I usually clip the black lead onto
an I/O screw, then take the single red lead in hand and
make my measurements. That avoids the possibility of
shorting the probe tips together.
Paul
Riffxyz
Thanks Paul.
I am sure you know what this is all about but I have no Idea about what
is Super I/O etc.However you have been very educational and have given
me some idea of what's involved.