Internal arcing and the story of how we got here

I purchased a k40 for $80. I ran it a few times to test it, and the laser was not burning. I held a paper in front of the first mirror and it burned through. The optics were my problem. I killed the machine, pulled the mirrors, spent hours polishing and cleaning the soot and aggregate off of them. I installed the mirrors, and set off to realign them.

Here is where things get funky. I was doing the far and near test with a post it note in front of the second mirror. I held the laser test button for 1 second and it would burn through the paper before I took my finger off. I moved my paper again, and tapped the test button again, and moved my mirror as needed. I get to the last mirror, and I did a double tap on accident and on the second tap of the test button the machine screamed at me.

When I press the button now it continues to scream at me. The question is, since it was working well before i double pressed the test button, could this be a tube error, component error, or something crazier?

Look like the insulation of your tube is damaged. It arcs to the body of the machine.

Arcs like this are not usually insulation failures although you should check to ensure that is not the case.

It usually means that the laser power supply is UNLOADED!

To likely reasons:

  • The tube is bad :frowning:
  • The cathode is not grounded to the frame properly.

Cathode not grounded to the frame? Would that be different than the regular ground from my 3 prong?

Is there a way to test the conductivity of the gases in the tube aside from mounting it and hoping it works? Can I meter the tube’s conductivity while the machine is off? Electrical metering and the likes are new to me.

There is a wire (perhaps green) that goes from the cathode end of the tube (the other end from where it arched). Trace it back and find out where it’s connected. Post picture.

If you have a miliamp meter it will go to it. Otherwise it should go to the FG connection on the laser power supply.

Do all this with the machine unplugged. The voltage on this laser is lethal.

1 Like

Also make sure the casing is properly grounded. The ground wire of some K40 lasers have been known to be connected via plastic washers or on the paint layer (instead of bare metal contact).


+1 @KenpachigoRuffy

Also, there’s a diagram showing this and discussion of it in our K40 “Getting Started” category, in the post that covers light and electricity safety: