Is my +5 rail overloaded?

[Ravynmagi]

I'm having problems with the USB ports on my motherboard and I'm starting to wonder if my power supply's +5 rail could be overloaded?

The symptom is if I plug in more than 2 or 3 USB devices directly into the back of my computer (or the front case USB ports) some of the USB devices will power off and stop working. It doesn't seem to be related to any specific port. I have 8 USB ports in the back and 4 in the front. And any combination of them seems to cause problems after more than 2 or 3 are used.

However if I use a powered USB hub, I can plug as many USB devices as I want into that.

I tried to Google what uses +5 rail. And couldn't find much, but kinda gathered that it is probably my fans, water pump, memory, hard drives, PCI cards and USB. I assume PCI-E isn't using the +5 rail.

Seasonic M12 700 watt PSU
5x 120mm Gentle Typhoon 1850 fans
2x OCZ Vertex SSDs
2x Velociraptor 300GB HDDs
2x WD Green 3TB HDDs
Soundblaster XtremeGamer PCI
4x2GB DDR2 1000 memory
USB backlit keyboard
USB mouse
2x USB game controllers
USB 3.5 hard drive (external power)
USB printer (external power)
USB hub (external power)

So, could it be the PSU? Or am I barking up the wrong tree with this?


PS. I plugged my computer into a Killawatt and with Furmark running both GPUs at 99% and using Large FFTs in Prime 95 on all 4 CPU cores, I measured 450 watts at the wall (quite a bit less than I was expecting). So I'm guessing overall my PSU does have enough watts.

 

[Zinn]

I don't know, but I've got to say... that is a killer setup!

If your problem disappears when using a powered hub, I'd stop worrying and love the bomb.

 

[kcmastrpc]

do you have a multimeter? if not, go to lowes and get a cheap unit.

test your voltages on the 20+4 connector (red wire = +5v, or pins 4, 6, 21-23). you can usually just stick the test leads into the connector to make contact with the pin sleeves. start pluggin usb devices in, watch the voltage, if you start dipping below 4.75 on the atx connector you have a problem with your power supply.

if you don't see any changes there, move on to the usb port itself. the two outside pins are your ground/v+. pin 1 is your +5v supply (if you dont get a reading, just switch your leads). if you see a voltage drop here then you likely have an issue with the motherboard or possibly an issue with a usb device drawing too much current (the last scenario is very unlikely)

 

[Tsumi]

It's extremely unlikely that you're overdrawing on the 5v line.

More likely is that you have an issue with your motherboard.

Pretty much the only scenario where modern power supplies can be overloaded on the 5v rail is using it with older computers with a high-end (for the time) CPU (pre-P4 era, where the CPU and other things mainly drew power from the 5v rail).

Also, if you were overloading it, your entire power supply would shut down, not just power to the USB.