Mac USB Problems

I’ve been having USB issues with my MacPro3,1. I’ve had the Mac Pro for about four years, but it’s otherwise been running like a champ.

A while back, I started having issues with a USB hub that was plugged into the back of the Mac. I replaced the cable, and things seemed to be fine. Until a while later, when the cable seemed to fail – then I replaced the hub, and all seemed fine.

Then the new hub was starting to have issues. So, I replaced that hub with another hub and new cable and things have been working swimmingly for a few months.

Then, this morning, all the USB ports on the back of the Mac seemed to go wonky – including one port which can recognize a device but always not power it properly. The front ports on the Mac, however, seem fine – sometimes.

I’ve zapped PRAM, I’ve booted into Safe Mode, and I’ve run USB Prober (from the Developer’s Tools) but… the prober tool doesn’t always recognize the device, either – but leads me to believe that every port is running as it should be running.

How could I, without introducing any new USB devices to the chain, be over-runing the system – especially when I’ve removed all USB devices and am still having issues with individual ones (like the wired Mac keyboard, but only sometimes in some ports but not at all in others)?

  • I can plug something like a USB flash drive into a port on the back and it might seem fine – it illuminates, but doesn’t always show a mounted drive (but always does on reboot, irrespective of port).
  • I can also plug Apple’s wired keyboard into a front port and it sometimes works, and sometimes doesn’t. It doesn’t seem to work at all in any of the rear USB ports.
  • I can see a Logitech webcam via USB Prober in one port, and its face illuminates when I open Photo Booth – then its face goes dark and Photo Booth doesn’t show an image.
  • If I plug that same Logitech USB webcam into just about any other USB port, the system doesn’t recognize it at all.
  • I tried reinstalling KEXT files, and that just forced me to reinstall Snow Leopard (which was painless, for whatever it’s worth). No go.
  • Someone in the comments suggested plugging my iPhone into ports to see if power was passing through them – and it was for all but the inner most rear USB port. Ouch.

I can’t imagine that it’s a failing power supply, but can’t help but wonder if I’m missing a software step after going through all of that. I’d hesitate to reinstall the OS only to find out the hardware was still the root cause. Who knows? Maybe Lion will fix the problem (and, at this point, I’m willing to wait a few more weeks for that install before either taking ‘er in or finding a Seattle-area Mac professional to help troubleshoot this on-site).

I believe it’s a hardware issue, but short of replacing the motherboard… ouch. “Repairs and Service Coverage: Expired.” Worse yet? Blake (from our community) sent me this link suggesting that this problem is known throughout my Mac Pro revision / line.