Carrying out a hard reset of a home KVM switch
Published on 20th March 2017 Estimated Reading Time: 1 minuteDuring a recent upgrade from Linux Mint 18 to Linux Mint 18.1 on a secondary machine, I ran into bother with my Startech KVM (keyboard, video, mouse and audio sharing) switch. The PC failed to recognise the attachment of my keyboard and mouse, so an internet search began.
Nothing promising came from it apart from resetting the KVM switch. In other words, the solution was to turn it off and back on again. That was something that I did try unsuccessfully. What I had overlooked was that there were USB connections to PC's that fed the device with a certain amount of power which was enough to keep it on.
Unplugging those USB cables as well as the power cable was needed to completely switch off the device. That provided the reset that I needed, and all was well again. Otherwise, I would have been baffled enough to resort to buying a replacement KVM switch, so the extra information avoided a purchase that could have cost in the region of £100. In other words, a little research had saved me money.
Yes, this is the hassle you have to go through to reset a KVM where one of the PCs has confused the USB hub built into the switch. As you say, it's because one/some of the attached hosts still provides a dribble of power.
It would be really helpful if there were a reset function to resolve this, or an option to NOT power the KVM from the hosts. I have bought a cheap 8-way to try to figure out how it could be modified, and I think it will require removing many (probably 16) diodes that gather power from both USB *and* video connections. It's a significant reverse-engineering exercise!