Just installed a new Cloudray PSU, did a engrave / cut, engraved fine but 2-3 seconds into the cut (higher power) an arc sound followed by a high pitch buzz. Now the tube is on whenever the machine it turned on.
Should I be looking at the PSU or tube? The tube was also only replaced last week and has a fair number of hours on it
Recheck the wiring for the tube. Make sure there’s no damage to any of the wiring and that you have a very good welll insulated connection on the anode side (positive).
Yes, it’s a definitely a good idea to check for any signs of damage to the wiring insulation on the high power side.
Do you have an ammeter fitted? What is the current when the machine is on? Set the max-power at the controller panel to something low, if you set it to 10% does that change the output/current?
Hopefully it is just part of the PSU circuit that is broken - the part that accepts the laser-on signal. If you were using the active high (TH) input on the PSU try switching the wire over to the active low (TL) input (or vice versa) and in the controller settings change your output signal to match (Edit > Machine Settings >Laser 1 Output Signal
I have ordered a replacement mini gerbil board, when I tuned the machine on with the PWM cable unplugged, there was np power to the tube, with the PWM plugged in, the tube came on as soon as the PSU did.
I also went and bought a 60W machine that someone local was selling, I will set that up and have that as my main machine for now and rebuild the K40 and either have it as a spare or sell it once its back up and running.
The simple fact that it worked, for even a short time, would indicate the the machine is wired correctly and that it’s configured right.
The proper procedure is to follow the signals… if the machine is lasing continuously, then the issue is either the lps or the control lines (signals) to the lps.
Is it being told to lase by these control signals…?
If you remove the control lines (unplug them) the lps, on it’s own, should not lase…
If it does lase, it’s the lps, if it doesn’t lase it’s the control lines (i.e. the controller or wiring).
Seems like you figured it correctly, as the controller. Congrats on the 60W machine. 
Good luck
