yep, it's the mobo. same experience here with my sunbeam fan. i connected 3 fans in the mobo (front,back,vreg). vreg fan is not controlled so it just worked like being directly connected and still will appear in hardware monitoring. the other fan is supposed to be ~2000rpm but was running irregularly at 800-1100rpm. At first, i thought my mobo was busted coz the fan works well when directly connected to psu. hehehe.. Then i figured, the Fan Speed Control was Enabled by default in the BIOS. I simply disabled it and, wallah, works like being directly connected to psu.
