Laser machine sparking/arcing what went wrong?

I have had my chinese laser machine for about 15months now and overall been pretty happy with it. I would say it gets used roughly for 3hrs a day 5 times a week. Judging by that i work that out to be some what 900hrs of tube use. A few days ago i switched the machine on and went ahead with some engraving, it started to make a loud ticking noise which i couldn't figure out where it was coming from. I left it to carry on so i could locate the noise, and found it to be coming from the laser tubes access door. I also saw flashes of light which i automatically assumed to be sparks so turned of the machine to further investigate. Got everything unpluged and lifted the rear hatch and noticed black burn marks on the casing where it must of been arcing. It had seemed as though the rubber seal had detoriated and caused the power lines to spark onto the case. So i did a bit of research on what kind of seal this may be, the closest i found was a "silicone compound to reduce the chance of high voltage breakdowns".
If this is the silicone that was used then why did it break down? How can i avoid it happening again? Is there a better method of attachment or quality compound that can be used.
I contacted the supplier and showed him the pictures and his response was "your tube seems to be damaged causing the arc" is this true? Is there anything that i could of done to prevent this?
Thanks

I am not sure what you are asking.

The insulation has deteriorated resulting in the HV arcing, this can be caused by mechanical friction (wear), moisture (humidity) or just electrical breakdown. Repair the insulation, reconnect and you should be back in business.

I think what the vendor was trying to get at is it's possible the breakdown was a symptom caused by the tube failing, since the startup voltage would be more likely to arc.

Zax.

It is not totally clear from the picture but it looks to me like the wire that protrudes from the laser tube is blackened. You probably have a poor connection there and the current will try to take the path of least resistance so sparks against the case. Clean up the connections and use some thick walled silicone tubing as an insulator.

I had the same problem. At first any air in the electrical tape seemed to pop with the high voltage. Then I tried silicon insulating materials on the casing etc which worked for a bit.

In the end I found rotating the tube round 90 degrees so the contact was vertical stopped it all.

Though like zax said your tube may have gone.

Yes my tube has now gone and it no longer fires. Magritte what silicone did you use to reseal the valve? As you turned the tube i am quessing it is further away from any contact metal? Does anyone know if the tube reached the end of its life and thats a normal effect of the silicone to break down due to higher startup voltages? Or is it due to missues? Lastly has anyone got any insitghts to any better methods of attachment. Many thanks for the responses.

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Originally Posted by c02laser

Yes my tube has now gone and it no longer fires. Magritte what silicone did you use to reseal the valve? As you turned the tube i am quessing it is further away from any contact metal? Does anyone know if the tube reached the end of its life and thats a normal effect of the silicone to break down due to higher startup voltages? Or is it due to missues? Lastly has anyone got any insitghts to any better methods of attachment. Many thanks for the responses.

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I just used some stuff called sugru because that was the only silicone I had. It looks quite similar to the stuff you have in the pciture. I covered the soldered wire with silicone rather than using tape. Not sure what you mean by the valve

Yeah turning it just meant it could no longer jump the air gap as easily.

The arc looks to be caused by the tube going I would say. Its very high voltage and has to go somewhere so has jumped to the case because the tube is mostly glass.

It sounds like the tube reached the end of its life and then the insulation breakdown and arcing resulted.

I prefer to make a clean solder connection and then either wrap in HV tape or use a HV rated silicone (most are), but it takes some soldering skill to do so well and not risk damaging the tube. Using a screw clamp is acceptable and much easier, others have successfully used croc clips or similar but I don't like them - personal opinion, no real data to support that they are worse.

Zax.

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Yes my tube has now gone and it no longer fires.

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From the PSU manufacturers sparse data they do say that the PSU can support some arcing to ground but not for very long.

Do you know if your PSU is still OK and working ?

Tweakie.

How would i go about checking the psu? The machine still functioned completely fine (moving the point to datum etc) prior to the disconection of the voltage cable to tube. I have ordered another tube and awaiting delivery. Just fear the carbon point the arc is caused and just hope i can rotate the tube as magritte advised, to avoid any further arcing?

Glue a ceramic plate or a piece of glass onto the chassis. I'm serious - I once repaired the arching HV supply on a TV set with a porcelain eggcup!

As you have already ordered a new tube it is probably best to wait until it arrives - that will test out your PSU.

When fitting the new tube try to get the maximum air gap you can between that HT connector and the chassis.

Tweakie.