Auto-firing tube, need help/idea


Quickly, I’ve bough a SOLO II from LightObject (LO) a year ago and 2 weeks ago the PSU burned on me. Not knowing if it was the tube or PSU at the time, I’ve bought both from LO (But a SPT 60w tube instead), no time to waste.

After switching the PSU, the laser was running fine again. So the original 40w tube was good to go but the tube started to auto-fire (sporadically or constantly) when in standby. I tried the new 60w tube, same thing.

What I know/tried:

  • Laser fire when lid is open, so lid safety is not working

  • Laser stop when the water pump is off, so WP is working

  • The HV wire is not close to any signals wires

  • Tried to skip the mA meter without success

  • The AC cable and Female AC connector were changed without success

  • AC ground is theoretically good. The laser have it’s own breaker (20A). Installed by a certified electrician. I also have another circuit just beside it, same spec. No success on both.

  • TH to GND : 1.08v

  • TL to GND : 4.65v

If anybody have an idea, please let me know. My company run 100% with the laser and I’m really stressed out at the moment.

Do you think the new PSU is at fault and DOA?


HI, you probably already checked but i would run through all your psu/laser wiring and make sure you still have good connections after the install. I had a loose wire once that when it rattled would cause the laser to fire. It could be the psu but idk. Maybe check your signal wire from your logic board(whatever type your using)

1 Like

Either the PS is failed or there’s some spurious signal tickling the input and telling it to fire when it shouldn’t. Would be a good place for an oscilloscope to poke at the control leads.

If you disconnect the control wires from the PS does it still do it?

I don’t have one…and I’ll not know how to use it anyway, haha.

When I unplug the signals wires from the PSU, it stops. So, the problem is probably coming from the PSU?

The 60w will trigger the auto firing more frequently than the 40w if that matter, for whatever reasons.

Auto firing can be a couple of things: poor signal grounding/connection; LOPT breakdown (the high-output transformer in the Laser PSU).

If you changed the PSU, put the original back and see if the problem recurs.

Did you calibrate the LPSU?

Random firing when quiesced is dangerous. If you have a separate switch for your tube, turn if off after a job.

Electrical noise can definitely cause it. You could put a 1000muf 40v capacitor across the signal + Gnd to catch any stray bumps from your AC supply.

An isolation power strip before your laser/cooler will rule out any external influences like boilers or freezers or garage doors.

If you have your chassis tied to AC earth using a separate cable from the back of the chassis, take it off. You should be earthed through the AC centre pin only. And all your gear should be on the same AC ring.

A True-RMS digital multimeter with hold and hi/lo readout is very useful in this situation. You an even get ones that attach to your PC and log their readings with the same timestamp as your job/control.

Indicates more that the problem is with the signal source. Something’s loose or contacting when it shouldn’t be.

Can’t. The original PSU is broken but before the breakdown, everything was fine that’s why I’m more incline of a DOA PSU. The laser was running smooth for a year. I’ll probably buy another one to test; always good to have a spare PSU anyway.

By calibrating you mean making sure the mA is good to go and all? Yes and that’s the only thing LightObject told me to do after installing the new PSU.

Always, I have enough tattoos as is, haha.

Grounded only by the 3 prongs AC plug.

Overall, the only thing that changed between before and after the problem was the PSU. So like stated, that’s why I’m more incline to push the DOA PSU idea. It doesn’t mean that it can’t be another thing though, so I’ll try your possible solutions.

Thanks a lot guys!

This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.