[SOLVED] Why do fan splitters have missing prongs?

[barkersofgeraldine]

I'm in the process of replacing my fan splitters and noticed that my old one has only 3 prongs/pins.

My new fan splitter arrived today and it is also missing a prong

Why is that? The pins missing are the ones connected to the "yellow" wiring

 

[NightHawkRMX]

That is a tachometer pin. It tells the motherboard the speed the fan is rotating at.

The tachometer pin on the motherboard can only accept one tachometer signal, so you cannot connect more than one fan to that pin.

 

[Paperdoc]

Exactly as NightHawkRMX says. All Splitters or Hubs do this one way or another. On the Splitters, the simple method is to omit Pin #3 on most output "arms" and include it in only one. This avoids confusing the pulse counter in the fan header with two or more overlapping streams of speed pulse signals. This has NO effect on ability to control fan speeds - the mobo does not use the speed signal for speed control. BUT it does use that to monitor for fan FAILURE, and warn you if it gets no speed signal from a fan. When you use a Splitter, the header can NOT "see" the speeds of ALL the fans and hence cannot monitor them all for failure. So from time to time YOU should check that all your fans are still working.