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RENAMED: Chassis Fan / PSU Fan issues

R

RTGMusicMan

Junior Member
I'm having a problem with a chassis fan; if it's connected to the 3-pin header on the motherboard, it never spins anymore, even when the CPU temperature escalates. If I connect the fan directly to the PSU, it works fine. If I connect a brand new fan to the motherboard, it also fails to spin.

The motherboard is an Abit TH7-RAID. Am I to assume that the connector on the motherboard has gone bad? Is there anything else I should be checking?

Thanks.
 
Checked that; the BIOS doesn't seem to allow me to enable or disable control of the chassis fan, though it does let me choose whether to monitor it. I've connected the fan directly to the PSU so the system still stays cool; I guess the connector's gone bad.
 
What's the Amp rating of the first fan you had connected? I usually won't hook anything over 0.4A to a mobo connector. Your manual or FAQ on the web site should tell the limit that your mobo's connectors can handle. IAC, I'd get a DMM (digital multimeter) and check the mobo connections.

.bh.
 
I can't find my mobo's limits in the manual or on the website, but the fan that was connected is rated at 0.38 amps, 12 volts, 4.6W. My multimeter reads 4.4V off of the mobo connector, so maybe the voltage is too low for the original fan; but the new fan, which also doesn't work off the mobo, only draws 0.30 amps. Unfortunately, my multimeter doesn't measure amperage, so that's definitely a possibility; or it could also be a faulty tach pin on the connector, or a glitch in the BIOS. I'm trying to remember when I noticed the fan fail, and if it was close to the time of a BIOS flash.

(EDITED FOR TECHNICAL ERRORS)
 
Alright, this may be the beginning of an impending power supply failure. The two fans (one 40mm, one 60mm, from the looks of them) inside the PSU itself are both rated at 12 volts, but one of the connectors inside the PSU is only giving 8.8 folts, and the other is only giving 4.8 volts. The PSU fans are visibly spinning slower than I would expect, and I have a feeling this is contributing to the rising CPU temperature. I have also added more hard drives and PCI cards to the system, so I may be pushing the limits of my original 430W PSU.
 
Power supplies, these days regulate their fans. (Yes, they undervolt them)

The 4.4v coming off your mobo header probably isn't enough to start your chassis fan. (Many won't start <6V.

Does the mobo header only supply 4.4v when your temps are high?
 
Computer fans are supposed to be 12V fans - if you are putting lower voltage fans on there you are probably burning them out and perhaps the mobo fan circuit as the resistance of a 5V fan is less than half that of an equivalent 12V fan (that needs the same Amps).
. The mobo fan headers (except maybe the CPU fan header which may be variable) are supposed to put out 12V. The fan's RED wire from the fan connects to the +12V the yellow wire from the fan is the tach or speed sensor wire and the black wire, as always, is ground.
. Most PSU fans these days are supposed to be thermally controlled, so the supplied voltage varies with the temp in the PSU. So those readings could be perfectly fine. Measure the voltages at an unused molex drive connector to see how the +5 and +12 are doing. Measure at the ATX connector for the other voltages.
.bh.
 
Originally posted by: xbassman
Does the mobo header only supply 4.4v when your temps are high?
Click to expand...

When the CPU temp climbs above 60 celsius, the header voltage goes up as high as 4.7 volts, but that's not much of an increase. At high temps, it still doesn't spin a fan.

Originally posted by: Zepper
Computer fans are supposed to be 12V fans - if you are putting lower voltage fans on there you are probably burning them out and perhaps the mobo fan circuit as the resistance of a 5V fan is less than half that of an equivalent 12V fan (that needs the same Amps).
Click to expand...

I mis-stated myself earlier (and I have edited my earlier post to correct it) - all the fans are 12 volts; the distinction I meant to make was in their amperage and wattage. The 5v leads on the molex connectors show up fine; but again, I have no way of measuring amperage, and the last time I had a power supply fail it was the amperage that had dropped, even though the voltage looked fine.

I feel like a complete NewB on this forum, so thanks to all of you for the suggestions and guidance. I think I may get a power supply tester and see what it says.
 
First of all, thanks again for all your suggestions and information.

I tested the PSU with an ATX Power Supply Tester, and everything checks out. All voltages and connectors are fine; it's just the one header on the mobo that still won't spin a fan. As a result of all this poking and prodding, though, I did notice that some IDE ribbon cables were blocking the chassis fans' airflow, so even though both fans are hardwired to the PSU, the CPU wasn't getting much cross-circulation. With the cables fastened out of the way, the air comes in the front, blows across the CPU's cooling device, and gets drawn out the power supply (which has dual redundant exhaust fans). The CPU's peak temperature under maximum sustained load dropped 9 degrees celsius.

Heh - never overlook the obvious.
 
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