I ran into a bit of a problem with my new Keyboard Video Monitor (KVM) switch this week, with an interesting solution. First, a bit of background. When I’m not working in my office in downtown Worcester or at a client site, I work from my home office. I like to vary where I work throughout the week, as I feel it stimulates new ideas and keeps my mind fresh. In my office at home, I have a desktop computer with a nice LCD monitor. My work computer, however, is a laptop. So I had the thought last week of buying a KVM switch so I could use the same keyboard, monitor, and mouse with my laptop when I’m working from home. So I picked up a great little TrendNet TK-207K KVM switch for less than $30. Quite a good deal!
Now for the snag… The KVM switch uses a USB mouse and keyboard, and then one USB cable leads to the PC. Thus, the switch acts as a composite USB device to the computer. This is very convenient for a laptop, as it means just plugging in a power cord, one USB cable, and a video cable. The problem came when I’d switch over to my laptop for a while. After several minutes, I’d hear the sound from the desktop of hardware disconnecting, and then when I switched back to the desktop, the mouse and keyboard would not work. No matter what I tried, I could not get the mouse and keyboard to work when I switched back to the desktop.
Now for the solution… My hunch was that this was related to some kind of power saving function on my computer, and that ended up being exactly the problem. I opened up Device Manager on my computer (via Computer Management) and found the "USB Root Hub" devices. If you bring up the properties for "USB Root Hub" and go to the "Power Management" tab, there’s a checkbox for "Allow the computer to turn off this device to save power." I unchecked that box and VOILA my problem was solved. I guess the computer was turning off the power to the USB port after it didn’t get a signal from the KVM for a while. Perhaps this is something that could be improved in the KVM, or perhaps this is simply how you’re supposed to fix the problem. However, in all of my searches online I could not find this solution.
So if you’re using a KVM switch and your mouse and keyboard stop working, check out the power settings under device manager.