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CPU fans spinning asynchronously - CPU exhaust fan is slower than the intake fan

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Hello there. Recently I noticed that my exhaust CPU fan pointing to the back is slower than my CPU intake fan, to the point where the fan will turn off completely for a few seconds then spin up a little bit again, before powering down again slowly. I've checked the cables but didn't find anything obvious, will try again. Also tried setting the fan curve in the bios with the fan curve optimization tool on the b450-f gaming motherboard, but is still acting weirdly. Will even turn off while gaming

The CPU cooler is a Cooler Master MA610P.

Any idea why something like this could happen?
 
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Check if your mobo has a desktop software suite you can install. BIOS typically offers basic fan controls.

If this isn't a hardware fault it mirrors the behavior of an efficiency setting that spins the fan down when the assigned temp sensors are low. If your cpu cooler is performing exceptionally well that would offer a partial explanation. Why the exhaust fan is doing this and not the intake fans is weird to say the least. Typically cpu/exhaust run independently but at a base speed they never drop below.

I'm one who always suggests a physical inspection - carefully reseating fan connector (on the correct 3 pins if not PWM) - never hurts.

Edit: I should try actually reading and making sure I comprehend the question before responding.
 
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Try another fan header and create a fan curve in the BIOS for it.

(I had an issue with my noctua exhaust fan stopped spinning on at the login screen, connected to another header, it seems fine so far)
 
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Another method is a fan splitter - if it does not mirror the other fans on the splitter it is the fan itself.
 
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Hi,
How exactly are they connected to the board, one in cpu and other in cpu assistane ports or splitter off one cpu port for both ?

Cpu assist ports act a little differently than cpu ports sometimes.
 
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Hello there. Recently I noticed that my exhaust CPU fan pointing to the back is slower than my CPU intake fan, to the point where the fan will turn off completely for a few seconds then spin up a little bit again, before powering down again slowly. I've checked the cables but didn't find anything obvious, will try again. Also tried setting the fan curve in the bios with the fan curve optimization tool on the b450-f gaming motherboard, but is still acting weirdly. Will even turn off while gaming

The CPU cooler is a Cooler Master MA610P.

Any idea why something like this could happen?
Is the fan a 3-pin or 4-pin. Is the board header 3/4-pin?
You said you set a curve in BIOS but what is the target/assigned temp?
Does the board has the option of zero rpm (fan stop)?
 
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I also had that exact problem and found that using a PSU cable for power fixed it. The fan header on the mobo was weak or faulty.
 
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If anyone wants a good fan control software, this is very good.
 
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Check if your mobo has a desktop software suite you can install. BIOS typically offers basic fan controls.

If this isn't a hardware fault it mirrors the behavior of an efficiency setting that spins the fan down when the assigned temp sensors are low. If your cpu cooler is performing exceptionally well that would offer a partial explanation. Why the exhaust fan is doing this and not the intake fans is weird to say the least. Typically cpu/exhaust run independently but at a base speed they never drop below.

I'm one who always suggests a physical inspection - carefully reseating fan connector (on the correct 3 pins if not PWM) - never hurts.

Edit: I should try actually reading and making sure I comprehend the question before responding.
tried the inspection. For some reason that wasnt apparent in the cpu cooler manual, my cpu fans have 2 cables running off of them. they both look like 4 pin PWM cables but one is short and the other is longer and merges (i assume) together with the other CPU fan's cable into a single 4 pin that connects to CPU_FAN. Dont know exactly why the fan needs 2 fans to get it running, its not an RGB fan.

Try another fan header and create a fan curve in the BIOS for it.

(I had an issue with my noctua exhaust fan stopped spinning on at the login screen, connected to another header, it seems fine so far)
tried CPU_OPT but then the system wouldnt boot. as for using a chassis fan header, i could, but the fan for some reason has 2 cables coming off of it which both look like 4 pin pwm which u can see here
 
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@Empecial

You know, that sorta sounds like you have one normal fan cable and one fan speed reducing cable installed.

Edit: After you edited to add the video starting to consider I might be using strikethrough on every post I make here.
 
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Another method is a fan splitter - if it does not mirror the other fans on the splitter it is the fan itself.
Might be. From what i understand (which the manual really doesnt make clear) it seems like the cable for the fan merges into another cable for the other fan which then gets plugged into CPU_FAN, so they should both be running the same speeds. but u can see here
that there is a second cable on the fans, not really sure what that's for

Hi,
How exactly are they connected to the board, one in cpu and other in cpu assistane ports or splitter off one cpu port for both ?

Cpu assist ports act a little differently than cpu ports sometimes.
The fans are both connected to a smaller cable in the middle and then to another cable that ends in a single output that connects into CPU_FAN like here

I also had that exact problem and found that using a PSU cable for power fixed it. The fan header on the mobo was weak or faulty.
Thats interesting since i believe both my cpu fans are connected to a single output cable that plugs into CPU_FAN. i'd assume they'd be the same speeds since they're in the same mobo plug, no?

@Empecial

You know, that sorta sounds like you have one normal fan cable and one fan speed reducing cable installed.
Here's the "merge" cable both the CPU fans plug into which plugs into CPU_FAN
and this is the small cable in the middle
 
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In my case, I actually have a bad fan header.
 
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One of the timestamps finally showed you can completely remove the fans and their power cable.

I'd try unplugging your front fan from it's known working header and plug the one running slow into it. You could also try the Y connector from cpu cooler with slow running fan and case fan on that same header and see if it is faulty.
 
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fair enough. which PSU cable did u use?
I think its an extension cable that ends in a fan header. A converter from a normal cable for Sata, etc. Its an older PC.
 
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