Hello all,
I need to set up the laser to “no firing”. At 0% power, it is still firing. Any suggestion to solve the problem ?
Might depend on how you wired up the controller. Most of the co2 actually require a pwm to limit the current value allowed through the tube. It also requires another control line referred to as laser enable. Most generic controllers don’t operate this way.
You can check all of these with a voltmeter for an operational value. No need to turn on the laser power supply (lps).
Is this a diy project?
That’s likely a result of not having a connection to the laser power supply’s L terminal to disable the laser.
A PWM value of 0% will turn the controller’s output transistor fully on, which means the voltage on the pin comes from the saturation voltage of the transistor and the pullup resistor in the power supply. For your controller, that’s high enough for the power supply to regard it as a constant analog input voltage high enough to fire the laser.
Assuming this is the doc for the MG3 controller, then it has a digital output to control the laser: “LO Output available via power connector compatible with K40 power connector layout.”
If that signal is not connected to the power supply, that’s the problem.
If it is connected, then it’s not working and some debugging is in order.
In order to test the lps, I unplug the signal cables and it doesn’t lase, so I think it has to be pulled down from the driving electronics to lase.
Most electronics that are a piece of something larger are built so if they aren’t connected, they are disabled. Don’t want to plug into something that could hurt you.
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AFAICT, the power supply pulls the H terminal low and the L terminal high: the “nothing connected” state is not lasing.
This is, however, a K40-ish power supply and I’m not sure what the rules are. If it’s been gimmicked to work with a GRBL PWM-only input, perhaps by having the control inputs tied active, then having that input not reach 0 V is the problem.
Although the standard advice for HV laser supplies is to disconnect the controller plug, then poke the Test button: if the laser fires, the problem is upstream of the power supply.
At least it won’t shouldn’t fire all by itself.
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Hello All,
I solved the problem. After having tried numerous things (grounding, $31=0), it was the 5 volt wire from the controlling card to the power supply that was loose.
Thanks for all the suggestions
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It’s always the connector! 
Thanks for telling us the solution, because somebody else will benefit from your discovery.