Problem with the laser tube current

I have a problem with the laser current. I have painted marks around the potentiometer. These marks matched the current. A month ago there was a shift. The potentiometer set to 10mA and the analog ampermeter showed only about 5mA. Today the potentiometer was set to 15mA and the ampermeter shows only 3mA. That’s too little to cut. A strange whistling sound is heard from the tube.
I heard this sound at low current before. It’s similar to this video:

I have 3 options

  1. Laser tube problem
  2. Problem with FLyback (my favorite)
  3. Problem with source board
    Do you have any experience with gradually decreasing current?
    Is there anything I can check?

Probably the flyback. What do you think @donkjr?

You can also see this post for a link to Don’s LPS troubleshooting guide. Major confusion: What's wrong with this thing (out of the box)!?

Definitely the sound of high voltage arcing. I would not run the laser with this issue as it can lead to damage to other sensitive electronics.

Check for arcing, open the tube door, start a small job, switch your room light off, and look for an arc near hight voltage connection on the tube. If so redo some silicone on the contact. (Remember a silicone tube was provided with the k40)


Today I looked at the tube. I found no arcing around the HV connector.

Ned Hill

Thanks, this is a very useful document, but it’s just a simple test. In my case, all systems working. Motors run, potentiometer can change power (0-3mA only), control board is powered and communicates with PC.

I made some video, please excuse the quality.

During 1 minute of recording, the transformer warpromed up to apximately 45 ° C. It is normal ? I’ve never tested the flyback transformer temperature before. So I have no idea what is normal.