60w Laser Tube strange internal arcing

[Steve Van Kley]

Hi everyone. New to the forum. I really like the information I find here. I have researched high and low for a process to determine the cause of my issue and haven't found anything really, so I'm hoping one of you here can help. :-)
I have 2 lasers, a 40w and upgraded a new (to me) used 60w Shenhui laser. I got a 'spare' laser tube with it when I bought it.

The problem: When i bought the 60w from a local here in the Tampa, FL area it worked fine for about 25 items, smaller etches and cuts. Power was steady and excellent, and the control worked flawlessly...and then I noticed during running an acrylic snowflake test, the power seemed diminished, so I raised the power 10% and noticed it had even less depth. I again raised the power another 10% and noticed that the power was still even less. This all on one run, over about 10 minutes.
I opened the back and noticed that on the discharge (cathode) end of the tube, the laser energy was 'flicking' from the normal center of the inner tube to the metallic wrap around the inside of the tube. It was still cutting the material, but definitely not as powerful as before. There is no arcing or any other unusual noise. Everything appears to be operational.

I have posted a video on YouTube here (http://youtu.be/lQub7BXF7JI) - So if any of you can please take a look at it and give me some advice, I'd REALLY appreciate it, I'm at a total lose now and very discouraged.

Steve

[Dave Sheldrake]

Ummm stop!

Get rid of the bubbles or you will kill that tube, if heat is building up that will reduce power by a huge amount very quickly before eventually killing the tube totally. The ARC doesn't look great but the bubbles are the bigger problem.

cheers

Dave

[Steve Van Kley]

Dave, I should've mentioned I DID get rid of the bubble after I took that video...sorry. The same thing is still happening.
What do you see that makes you say the ARC doesn't look great? I had thought a purple arc was normal.

[Dave Sheldrake]

It is, Pinkish / purple is fine but they usually don't go that far down the electrodes, not brilliant but not always terminal, I'm wondering if the current is too high? does your machine have an ammeter?

[Steve Van Kley]

It does not...as far as I know. It has the original LCD display, but I believe that's just for the controller. I did buy a mA digital display ut haven't received it yet. From what I've read the current should be <30mA, is that correct? I have a Fluke, so I could put it in series with the cathode end wire and see what I get - that should work, correct?
That brings up a question about my original point. You mentioned the color and length of the visible laser...where can I go to find info about that and other CO2 laser diagnostic information?
One last point, I did carefully look again at the bubble area, and there still is a VERY tiny buble there, but even inclining the laser at a 45 degree angle upward did make the bubble go out the outlet tube.

Thanks so much for your help Dave!!

Steve

[Dave Sheldrake]

No problem :)

Digitals tend to fall over when measuring current on lasers but it may give you a reading (black wire in series) no more than 22mA though....30 will kill it very quickly!! get a analog (needle)meter if possible, they tend to cope with the spikes a little better.

As to finding out about lasers...lots of stuff round the web but "Sam's Laser FAQ" can be very useful as well as a multitude of public forums.

cheers

dave

[Steve Van Kley]

All the brilliant people on here and no one has any thoughts/suggestions? :)

[Rich Harman]

From what I've read the current should be <30mA, is that correct? I have a Fluke, so I could put it in series with the cathode end wire and see what I get - that should work, correct?

You want the meter in series with the wire that attaches to the end of the tube where the beam exits - the end opposite what you showed in your video. Otherwise you will be putting 20kV+ through the meter.

My guess is that your tube is dead/dying.