Board: C3D Laser Board
Firmware: _Smoothie released late 2019
This may be something to move to facts
Problem: The 2007 iMac (El Capitan OS) and 2011 iMac (High Sierra OS) would not communicate with my Laser Board Via Light Burn.
Solution: The 2011 and below iMacs come with 2.0 USBs. You will have to use a Thunderbolt 2 USB dock to to upgrade the USBs to work.