Determining what to replace when USB port doesn't work.

The USB 3.0 port on the right side of this unit doesn't appear to be working. Plugged a Logitech Unifying transitter, which was not recognized. Tried a USB external Hard Drive to no avail. Same with two different external USB DVD drives. All of these devices work on the USB port off the left side of the unit. I dont think there is any power. I tried reseting the SMC and NVRAM, but those fixes didn't work. For the moment, we are using a USB port expander on the working USB port.

Nothing unusual with the unit. No spills or drops. Just sits on a desk and has been a very reliable unit. We replaced the Lithium battery and one fan a while back. It's worked fairly flawlessly.

Basic question: What's the best way to determine what needs replacing? I looked at the I/O board fix, which suggests two cables and a small I/O board. Unclear if I need all of them.

Is it possible there is something more simple that can be done?

I don't want to spend a lot of money if I don't have to.