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Bizarre electrical issue with USB hub powering PC case fans

Tags:
  • Components
  • USB Adapter
  • Power
  • Motherboards
  • PCI Express
a b V Motherboard
October 13, 2014 9:23:29 AM

Configuration:
Intel Core i5 3570K running at stock speed
32GB dual channel DDR3 (supposedly 1600MHz but Speccy reports it running at 799Mhz)
ASRock Z77 Extreme6 motherboard
250GB Samsung Evo 840
2TB Seagate HDD


As I start this thread, I noticed the discrepancy with my RAM speed, so I'm going to have to look into this. That seems to be a deviation from what it is supposed to be.

However, the original reason I came here is to ask about what appears to be a reverse power leak from a USB hub into the motherboard.

Yesterday I unplugged my PSU from power, and opened my case to clean out the dust (of which there was surprising little). Imagine my surprise when one of the two front case fans was silently spinning. Did a few double takes and eventually I pulled all the USB cables into the machine. That stopped the fan.

Then I did a bit of troubleshooting and found that a powered Hoo Too 3.0 hub was leaking power back into a Hoo Too PCIe USB 3.0 adapter.

For now I removed the power from the Hub (I need the hub), but I'm not sure whether to replace the hub or the PCIe card? Any opinions? I do believe the USB hub should not pass power back up the connections, but surely there has to be a fault on the PCIe adapter card as well to pass that power back into the motherboard?

I will be looking if I can figure out why and how the 5V USB power is leaking into the 12V fan circuits - that is totally wrong and I'm wondering if I should be looking to replace the motherboard as well.

Any opinions on this issue would be welcome.

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