The ground from the laser power supply needs to be connected to the ground on the SKR - can be on the power input or one of the ground pins available. Doesn’t matter, just need to have the grounds connected. On the laser side, there are two 24v in, and two grounds. All must be connected to their respective power connections.
I run a single 24v wire and ground up to the xlr plug on the Z axis, and then connect both 24v and both grounds for the laser to those pins.
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