Power supply or tube?

Im new to laser engraving. I recently bought a k40 chinese blue and white used. The P.O. said he never turned it on. It sat for over a year. Last night i turned it on ( after going through all the connections and getting the cooling water going). I set it to 7mA and test fired the laser ( into a post it note) just to see if i had anything. The laser does fire. But if i turn the power any higher, the laser doesnt fire. Is that normal or is there something i need to check? The tube isnt cracked ( no water in the tube or on the machine). Not sure if this bit of info has any bearing but when i went to look at the engraver, to show me that the laser did in fact have power, he cranked the pot all the way up and hit the test fire. A couple times. Im not sure if that could’ve done any damage or not. Thanks for any help in advance!

Welcome to the forum TJ!

That is not normal, we have some experts on here who will no doubt troubleshoot this for you (it’s not me!).

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Although I would not recommend it, you can fire the laser a couple of times with no coolant without damage. However best to run coolant before doing any other tests with the laser on.

{quote=“Tooj, post:1, topic:82359”]
But if i turn the power any higher, the laser doesnt fire. Is that normal or is there something i need to check?

That is not normal. At the point where the laser stops firing (and beyond) what does the MA meter read.

The laser stops firing around 10mA. From that point and above i cant even mark a piece of paper. I had a few pieces of blue painters tape on the 1st mirror and i did get a tiny dot, but i also had to hold the button down for roughly 7-10 seconds.

What I’m interested in understanding is what the tube current is doing as you increase the power setting.

When the tube stops firing at 10ma and you keep increasing the power setting:

  1. does the current reading get higher even though the tube is not firing?


  1. does it stop firing and the current decreases or stays the same.

  2. Do you hear any crackling, sparking or arching as you pass through 10ma???

Pease post a video of the tube as you test fire at and above 10ma

This is 7mA.

This is 10mA

This is 15mA

And to answer your question, ( sorry i forgot to put this in my last post)the laser seems to fire but makes no marks. The current doesnt drop or change when i press the test switch. And you can hear in the video, it doesnt make any real sound ( just the buzzing of electricity).