Help Needed, Please

I need some technical help. The output from my laser tube quit suddenly in the middle of a job. I cleaned the posts on both ends of the laser and jumpered across the laser switch. Nothing. I show a green power light on my power supply (for whatever that’s worth). Can someone with electrical technical skills give me ideas of how to diagnose this problem? Laser tube shows intact, and as I understand it, laser tubes just slowly run down. How do I test the power supply without blowing myself into the afterlife?

Any help is very much appreciated.



Tubes die slowly but LPS die suddenly.

NP… lets get started!

Post Pictures of:

  • Control panel front and back
  • Pictures of the connector side of the LPS

The green light on the LPS means that the supply has AC power and the low voltage is at least present.


  1. Does the laser fire with the test button down on the supply?
  2. When you push the test button down on the LPS
    a. Do you hear any crackling/arcing noise
    b. Is the tube lighting up

Hi Don:

Laser does not fire at all; no excitation of the tube whatsoever.

No arcing. Test button does nothing.

I’ve downloaded a schematic, and I’m competent with a VOM and I know enough to stay away from 15K volts. I would assume there’s a capacitor in there, too.

Actually it’s more like 22,000 volts but if you get zapped you won’t know the 5K difference :).
Just stay away from the output of the LPS and the anode of the tube.

I am guessing your LPS HVT is toast… sorry.

The test button on the LPS bypasses all other controls other than the IN. So pushing it eliminates most external problems.

Lets test the “IN” function;

Set the “Current Regulation” pot to max.
With the DVM set on DC volts measure the voltage on the IN pin relative to ground. With the pot at max is should read 5V.

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Yeah, I’m getting the feeling, too. Thanks for looking into my problem.


What is the IN voltage measure in the test above?

I’ll have to check tomorrow; life is getting in the way.

The way the laser died, it sure feels like a LPS issue. I cleaned and check all the terminals; I just can’t imagine a laser tube quitting with such abruptness.


Hi Don:

“IN” voltage = 5v
5V terminal to ground with amp meter full rotation = 5V

However, the 24 V terminal on P1 initially reads around 11V and rapidly decays to 1V. As I read the schematic, this should be constant 24V. This, I would guess, is were the problem resides.

Does that seem reasonable to you?

Also,jumpering across the terminals as shown does nothing.


I always remind everyone that there is no foolproof way to test this LPS and the problem can be the LPS and tube.

However, the HVT [high voltage transformer] is typically what goes and that is where the 24V is also developed from. Sounds like a bad supply.

That said do you have a stock controller and have not added on a 24 supply?
If so I wonder why you are not seeing some motion problems?

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No, motion with the stepper motors is fine. And my k40 is all stock.

I took the plunge and ordered a new LPS. I strongly suspect it’s the HVT. Thought I’d start with the least expensive possibility first. I dread buying a new tube and having to fiddle with mirrors to dial in the laser again.

Thanks again for your input. Let you know what I find.


ok, let us know so we can mark this solved.

If it’s not the LPS you have not wasted much as it is a consumable part anyway.

Don… your analysis was correct. It was the LPS; when I pulled the old one, there was considerable discoloration around the transformer. I just finished installing the new one and it test fired fine.

Thanks again,



Good deal… another correct LPS diagnosis added to the pile !!!

Glad you’re up and running again!

2 posts were split to a new topic: Does using the 24V supply shorted the life of the HV supply?