Laser Tube Diagnosis Help: Small Spark, No Pulse

Hi everyone,

I’m trying to get a G570 laser cutter working for a high school robotics team - it has sat unused for several years (manufactured 2017), so I’ve spent about a week doing maintenance to get it running again.

The laser tube worked for long enough with the “pulse” button on the control panel to calibrate the optics, burning holes in paper. However, it stopped during the first cut. Now when I hit the “pulse” button, there is a faint high-pitched sound from the PSU (unsure if that was there before) and this small spark at the negative electrode (instead of the expected plasma glow). Each video shows two 0.5s pulses from pressing the button on the front control panel.

Do I have a dead tube or PSU? This is a non-profit team so I don’t have the luxury of just swapping one/both out and seeing what happens, I’d like a confident diagnosis before we make the purchase.

Some things I’ve checked:

  • Water cooling is fine, a CW-5200 is keeping it at 20C and the water flow sensor is working.
  • Wire connections externally from the laser are fine, electrode terminals are insulated with a vinyl tube and silicone caulk, as it came from the factory.
  • There is no obvious/dramatic arcing to the body.
  • There is no water where it shouldn’t be inside the laser tube.
  • I spent some time looking for cracks and I was unable to find any.
  • The laser PSU fan is spinning. The “test” button doesn’t pulse the laser, but I’m not sure if the same spark occurs, since I was the only one in the shop.

Thanks in advance for your help!

If it’s this one, it’s likely a Ruida controller, such as a 6442 model.

Uses a 2" lens as stock.

These tubes fail over time, used or not… I’d suspect the tube has a problem.

This is my lps,

The unmarked connector on the left is for power to the lps.

I remove the right hand signal connector (green) and use the test button (red) for a 100% lase. That will test the lps/tube.

There is no simple way to eliminate one or the other from the combo.

Good luck


1 Like

Tubes do not go bad instantly.
The spark is the laser trying to lase.

Therefore the LPS is likely bad…

Sorry, no such thing when the tube and LPS are suspect :disappointed:.

That said, the symptoms [and lots of experience] suggest to me the LPS has a Shorted transformer (HVT).

Post pictures of the machines:

  • Control panel
  • LPS showing wiring.

Thank you both for your responses!

It is indeed a Ruida controller, unfortunately I don’t have a picture of the panel and I don’t get back to the lab until later next week.

Thanks for the tip, although I suspect the fact that I see a spark in the tube from the control panel pulse indicates that the signal is making it to the tube already.

Noted :sweat_smile:

That’s good to know, it was indeed a sudden failure from cutting to not cutting.

Noted once again :sweat_smile:

I appreciate that, I do feel a lot more comfortable just purchasing a replacement LPS. Unfortunately I don’t have a picture of the LPS, but I believe it’s the DY10 80W based on the blue outside case and the connectors. I’ll start a replacement with this for now and take advantage of Amazon’s generous return policy :slight_smile:

Will update end of next week, thanks again!

Apologies for the late update, this took longer than expected.

tl;dr Swapping the LPS fixed the problem!

Here’s a photo of the laser power supplies (right: broken, left: new)

I have no idea what the old LPS was, but I replaced it with the Cloudray 80W. I suspect this is a higher wattage than the old one (I see two transformers instead of one inside), but I also have no idea what wattage our tube is, since the label on the tube was left blank and we have no documentation remaining from time of purchase.

I did end up having the re-wire everything. The pin-outs were different for the signal connector and I had to re-terminate the AC wires. The new LPS also came with high-voltage wires that I chose to re-attach to the laser tube instead of splicing with the existing wires to avoid bad insulation. I was surprised to see that the laser wires at the end were simply wrapped around the tube terminal posts underneath the piece of silicone tube and caulk… I did the same but very quickly added a small amount of solder to keep the wire from unwrapping. I avoided transferring any heat to the terminal post, I’m sure that’s bad for the glass laser tube.

All in all it was a relatively painless replacement, and we’re very happy to have the laser cutter cutting again! Thanks again for your help!

Bonus photo of the electrical panel inside with the LPU removed - the smaller green connector on the left was re-terminated (AC power wires and the laser tube negative wire) and the longer green connector on the right just had its wires moved around to match the new pinout.

Do you have any way of monitoring the tube current?
The more capable supply could allow you to overdrive the tube which would shorten its life.

A good rule of thumb that I’ve been using for my laser years and seems pretty accurate is this one. You can get a guesstimate of your tubes power as it’s related to it’s length…

@donkjr suggestion for the inclusion of a mA meter is honestly a worthwhile investment and is well worth the effort.