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Please help, I'm about to break something (PWM problems)

post #1 of 4
Thread Starter 
Hey guys, this is literally driving me insane. I can't figure out what the heck is wrong.

I have 9 PWM fans. I have two 4-fan PWM splitters from Gelid, they have one cable with RPM return each and are molex powered.

My motherboard is an Asus Sabertooth 990FX R2.0. It has two PWM fan plugs, CPU and CPU_OPT. I can plug in ONE PWM splitter to either plug. Works good, 4 fans are controlled, doesn't matter which one. I can plug in ONE PWM splitter and the loose single fan using up both plugs, works good 5 fans are controlled. If I plug in BOTH splitters using each of the plugs, all of the fans decide to go to max RPM. They each work individually in both plugs.

I can't even imagine what the problem is. There is no way for the board to know how many fans it is sending the signal to, it doesn't care as long as it gets one RPM back per channel. Since they are molex powered I seriously doubt 4 fans on each header is overloading what the board can do. Does anyone have any idea what is wrong here?
post #2 of 4
You are correct expecting it to work properly. Are both the fans that are connected to the rpm wires the same? I don't think it should matter but it might. The other fans don't matter (if they are the same or not) but the 2 fans that have the RPM return may need to be same/similar.

I do not have the problem you are having on my p8z68-v gen3 and I never experienced a problem like that on my Sabertooth 990FX but on my 990FX both RPM returns came from identical fans.
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post #3 of 4
Thread Starter 
All of my fans are identical, Bitfenix spectre PWM's. I think they are actually the problem altogether. I dug out 4 NXZT PWM fans and 4 Corsair PWM fans of both 140 and 120mm sizes and they work perfectly populating all spots on both headers+splitters. I guess the Bitfenix fans will have to get returned. I wonder why they don't work properly?
post #4 of 4
I do not know everything about the PWM signal but it is possible that there is some slight current draw to it and the fans are just sucking up too much of it.

No clue really though. I am glad you kind of found a solution.

A great fan for the price is the CM Blademaster. They can be found for $10 a piece. I get all my fans at cost and so for the most part I only buy the Excaliburs but I don't really recommend them for anything except radiators. I can recommend a Blademaster for pretty much anything. They are only a little slower than the Exaclibur and that small difference in speed is a huge difference in sound.
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