Why might one USB port be problematic on a MacBook Pro?
Solution 1:
It's difficult to tell if you have a hardware issue or this is just how things are designed.
Have you read through this article on how Apple detects the first device that requests higher power and enables that power on some, but not all ports?
- Apple Computers and Displays: Powering peripherals through USB
I know you have linked to it, but the 500 mA is subject to measurement errors on the computer side - so plugging in a device can draw more current than the device says it should. Similarly, the measurement side where the Mac determines the actual power draw could be flakey or failing. This sort of thing isn't tested in the system diagnostics. You would need a test set / oscilloscope / engineering lab to really measure these currents with enough resolution to pin down exactly what is happening.
It could be just the order in which the system decides to detect a device attached. Once you have ruled that out and have a repeatable issue - you might need to have the Mac checked for service if it isn't producing power as expected. Now that you know that the order in which devices are plugged can affect things, perhaps this will help narrow down if the enhanced power is correctly available to some (changeable) subset of the ports and hubs made by Apple.
There is no easy answer other than being precise and narrowing down exactly which devices are causing errors and statistically determining/isolating whether it's the devices or the port that is out of spec and needs to be replaced.
Solution 2:
The port may be dirty or worn.
In that case it may be a contact issue, the port might have dirt, corrosion, etc. building up on the contacts. I would try cleaning the USB port with an electrical contact cleaner or isopropyl alcohol and see if the problems persist. If it does then I would suggest there may be an issue with the USB controller or the physical port itself, causing the misbehavior.
Also a helpful source on how to clean a USB Port
Unplug any devices from the USB ports and turn off the computer.
Blow compressed air into the USB ports to remove any dirt or dust.
Dampen a cotton swab with a small amount of isopropyl alcohol and squeeze out any excess.
Wipe the inside of the USB ports gently with a cotton swab. Allow the ports to dry for an hour or two before turning the computer on.
Read more: How to Clean USB Ports | eHow.com http://www.ehow.com/how_8279912_clean-usb-ports.html#ixzz21djdUf2f
