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4-pin CPU fan causing shutdown problem

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4-pin CPU fan causing shutdown problem

Postby FrankF » Sat Apr 10, 2021 5:35 pm

I've tried installing a new 4-pin CPU fan in an old PC with a whiny old 3-pin fan with a 3-pin header on the motherboard, and I get a "fan error, PC shutting down" message at bootup, followed by a rapid shutdown.

The new fan spins up fine, so I tried swapping pins 3 and 4, thinking that the "signal" and "PWM" wires had somehow got reversed, meaning the PC wasn't seeing the fan, but to no avail.

Obviously, pin 4 on the fan is not being used, but should I have just gone to Radio Rentals and got a 3-pin fan?
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Re: 4-pin CPU fan causing shutdown problem

Postby N i g e l » Sat Apr 10, 2021 5:57 pm

not enough info to help. is it a DELL ?

https://www.dell.com/community/Optiplex ... -p/7441036
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Re: 4-pin CPU fan causing shutdown problem

Postby FrankF » Sat Apr 10, 2021 6:18 pm

Blimey, that's a cautionary tale: dodgy old Dell, eh?

It's a 17 year old HP desktop. From what I read I just assumed that 3-pin wiring was more or less a wordlwide standard (except Dell!), so that pins 1 and 2 are earth and live, 3 is signal / tachometer (to tell the PC what the fan is doing), and 4 is PWM to enable the PC to control fan speed.

There are no pin IDs on the mobo header, and I don't have a wiring diagram for the (cheapish) new fan: since it spins up OK, I'm assuming the earth and live wires are correct.
I'm guessing that wire 3 isn't talking to the PC for some reason, which is why it keeps shutting down.
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Re: 4-pin CPU fan causing shutdown problem

Postby FrankF » Mon Apr 12, 2021 10:16 am

Anyone got any ideas for this?
I'm guessing that the fan is defective, even though it's spinning up fine.
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Re: 4-pin CPU fan causing shutdown problem

Postby Wonks » Mon Apr 12, 2021 2:27 pm

If you'd reversed the fan connection, then it wouldn't spin up, so that must be OK. Which means that the fan probably isn't sending a tacho signal back to the motherboard.

Can you take a photo just to check how you've connected the fan to the header pins?

Have you any utility or BIOS setting which can set the fan's speed to 100%, so that the tacho reading should then correspond to the signal it thinks its sending out, in case there's a speed mismatch shutdown going on?
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Re: 4-pin CPU fan causing shutdown problem

Postby FrankF » Mon Apr 12, 2021 3:24 pm

Wonks wrote:
Can you take a photo just to check how you've connected the fan to the header pins?
The connector (4-pin) and the header (3-pin) are both notched, so there's only one way to connect the fan: pin-4 on the fan is not being used, it's just hanging in mid air, as it were.
I mean, I'm not using a pin adapter of any kind.
Could that be the problem, perhaps?

I've just checked the BIOS, incl. Advanced: there's nothing about fans or fan speeds, so I'm assuming it's "Full Speed Ahead" or nothing.

Maybe I should just cough up for a 3-pin fan and assume this one is incompatible, but it bugs me not to know why. :roll:
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Re: 4-pin CPU fan causing shutdown problem

Postby merlyn » Mon Apr 12, 2021 3:39 pm

One possibility is that 17 years ago motherboard designers didn't imagine fans would spin so fast and therefore draw so much current. I have noticed fans initially spin up at a speed that is faster than the speed they run at in normal operation.

So when this new fan does that the motherboard is getting an out of range reading.

Not the fan, or the header but an incompatibility between the two that has arisen sometime in the past 17 years.
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Re: 4-pin CPU fan causing shutdown problem

Postby FrankF » Mon Apr 12, 2021 6:46 pm

I like that theory, so I just checked the potential current draw on the old and new fans, and the new one can draw more than twice as many milliamps, so you may well be right. :clap:

Anyway, I've just ordered a 3-pin fan with low current draw, so we'll see what happens.
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