I have 5v across the in pin when the machine is idle
@Alex_Krause Do you have any idea what should be the current to get the max. laser power?
If voltage is reducing ,that could be due to low current, right?
Voltage reading for max power? I can’t test for current without disconnecting wire and putting my meter in series with the circuit. I have been told not to exceed 18ma of current on my overdriven 40w k40 tube… which is more like a 30-35w tube. So being safe I typically don’t drive it more than 10ma to keep longevity of my hardware
I know there are a few different power supplies for the K40 some pull down and some pull up to initiate fire
@Alex_Krause okay thanks 
@Alex_Krause please identify your PSU, maybe we could find any technical documentation. (and find out how many different we have).