Friday 27 December 2019

Solved - Av Access USB prevents system boot

In a previous post, I'd detailed my setup of using a  4KEX100-KVM  to extend an unRaid VM to a very remote screen over ethernet.

This has worked out great, with one exception. With the Av Access transmitter USB plugged in to my server, the system would not post. It was necessary for me to unplug the USB, wait for post and unRaid to start booting, then plug the USB back in.

This was a chore, especially as my server sits in my attic and can be a pain to access.

I was living with the issue as thankfully I don't need to reboot too often, but in researching something else recently, I came across a known issue with some older USB devices. It turns out that some USB devices feed +5V back to the host adapter. This can result in some motherboards failing to post - my symptoms exactly.

The extreme solution is to sever the +5V wire in the USB cable (!) but before going that far, I decided to try placing a USB hub inline between the USB host adapter and the transmitter unit. Hey Presto! I can now boot and reboot without issue.

All hail the interweb.


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