Tube or power supply... or something else

[Steve78]

Hi folks... could really do with some advice here.

Had an LS6090 for a few years now, gets a tremendous amount of use and the current 60w tube was fitted last feb..

Tube has been great until today when cutting dropped to a scratch, then to barely a mark in a matter of minutes.... internal arcing right at the end near its exit from the tube... not jumping about, just steadily arcing to one spot on the side of the tube (I have read that this is sometimes normal behaviour in cheap tubes, which im sorry to say mine is, but that doesn't ring true)... the beam within the tube seems to be fluctuating in intensity and is a dull purple... accompanied by a fairly quiet crackling at the internal mirror end.... almost nothing getting out of the tube itself other than two barely detectable splits of laser... and finally, i spotted what looks like a hairline crack and the mirror end of Tube, so turned machine off and tried to run my finger across to see if i could feel a crack... guess what... electric shock from the glass... not severe, felt like a strong static shock, but definitely a shock... feel free to tell me that was stupid

Okay... options... ruined Tube? Power supply? Cooling? (im using tap water and not distilled) but i am running a chiller.... anything else?..... I'm edging towards tube as it has had at least 1200... probably closer to 2000....hours of use and is a cheap brand, but the crackling, the shock and the fact it died so quickly have me concerned

Desperate here as my business is entirely dependant on a working laser cutter... I'd appreciate any help... he'll, first person to correctly identify my problem and give sage advice on the fix can have one of my products in thanks.... steve

[Daven]

Hi Steve,
Sounds like tube - possibly overheated and cracked - check water supply is ok and if any water in outer part of tube.

Power in the capacitors can take a while to discharge so it sounds like there is a leak from inner tube to outer and the power is finding shortest route to earth

Give HPC a call to confirm
Best
Dave

[Steve78]

Thanks dave,
Already spoken to hpc... they indicated most likely the bulb but couldn't rule out the power supply... I've ordered a new bulb... should arrive in about a week

I agree that all indications point to a cracked bulb... can't see any water leakage but its difficult to tell. The aforementioned shock is whats concerning me... my science knowledge is shocking (no pun intended) but would i be right in thinking that the arcing beam to the side of the tube has probably charged the h2o in the outer tube and what i recieved would likely be static discharge?... or does the shock mean theres a problem with the earth wire?
Steve

[Daven]

It is hard to say - the power supply can go and the tube fails at the same time and vise versa. Saying that I have only had one PSU go but many tubes.

My guess (not qualified to do other) is the tube has failed and the arc is finding the path of least resistance - if the machine was off when you got the shock it would be residual power in the capacitors. Deionised water is best as it is not conductive - using normal water means the power can be conducted back to the chiller etc.

Also the minerals in tap water could build up in the tube especially in the older tubes that have aluminum couplers, the output coupler gets partially blocked overheats and the cracks or falls off (in some cases). One tube I had did this - it would cut ok - overheat and gradually stop until it cooled down!

Best
Dave

[Steve78]

Thanks... still waiting for my new bulb to arrive... likely to be a week..

In the mean time ive drained the chiller, flushed fresh water through and got some deionised water from Halfords ready to go in when the bulb arrives.

What's still concerning me is that if we're both guessing wrong and the power supply is faulty, what are the odds of it ruining the new bulb the second its turned on?... I dont really know much about these power supply units (big shock huh lol) and i would guess that its one of those devices that either works or doesnt (I.e. i get a beam or i dont) but opinion seems divided on this... last thing I need is to end up having to buy a new power supply AND another bulb.

[Steve78]

Oh... important NEW info that may help a lot with diagnosis..

While I own and occasionally operate the machine, my time is mostly taken in the designing of products and selling... most if the physical operating of the cutter is done by my business partner (who also happens to be my dad)

Now, we do clean the machine and extractor regularly, but whilst I was aware that we were using tap water in the chiller (which will from now on be deionised), he confessed a couple of things today that i wasnt aware of... namely that he doesn't check for bubbles each time the machine is turned on, and also that he hasn't changed the water in the chiller since February because he couldnt figure out how to drain the chiller.... (I know, but hes in his 70s (I.e. proud and didn't want to admit to it, so just had to be understanding about it)

I had a look in the bulb and its full of particles floating around, stuck to the glass and flecks of what i assume to be lymescale clinging to any imperfections in the tube.

Based on this discovery, would that increase the likelihood that its simply a knackered tube through misuse and/or neglect?

[Daven]

That would make sense. A bubble by the output coupler is worse as it gets hotter there so could have created a small crack but I would expect to see water in the outer tube. The newer EFR tubes are better for not trapping bubbles.

If the power supply was at fault I suspect the arcing would not have occured, the tube is the weakest link in the chain and is most likely the issue.

Have you fitted a new tube before or is HPC doing it?

The older versions of Dad can be temperamental, memory fades and the logic chip gets confused. As there is only Mk1's available and not really interchangeable there is not a lot you can do but treasure them. They do have their uses and I miss mine

Best
Dave

[Steve78]

Thanks dude

I've fitted a tube myself before... was simple enough so ill do same again... on that topic though, a thought occured to me... soldering those wires was the trickiest part and also not that fond of having such a heat source nest to the tube... is it safe to use terminal blocks or crocodile clips instead of soldering? I realise that they would need to be insulated afterwards, but was wondering if they would be appropriate or if they would be insufficient or even dangerous to use with that level of voltage... I had assumed that it would be maximum of standard 240v running through, so i nearly had a bloody heart attack when i looked into it and read that there are about 50,000v running through the thing... unless ive misinterpreted what people were saying of course lol

Message understood about dad mk1.... they're a bit like Alfa Romeos.... theyre very annoying most of the time, but if someone were to take it away.....

[Daven]

Don't solder! I use a terminal block cut out of the plastic. So much easier and safer. Wrap plenty of insulation tape as well as silicone hose.

The last tubes I had were already wired so just had to join the cable in the machine - cut enough insulation of both ends, slip one end through a few inches of silicone tube, repeat with heat shrink. hook bare cable around each other like a figure of eight and twist the ends, solder the joint. Slide heat shrink over join and shrink. wrap with insulation tape. Slide hose over joint and wrap again - jobs done.

if the insulation is not enough you will see or hear an arc discharging to the cabinet.

Don't over tighten clamps - I like to be able to twist the tube to ease the bubbles out of the input coupler.

Always make sure you are working in a safe way - the machine should be off for a period of time to allow the capacitors to discharge (there may be a way of doing this but we cannot recommend doing so here)

As for power yes it is in the range of 50,000v but I think DC - still enough to worry about! If anyone is concerned about fitting a tube then call HPC as that is really the safest way

Best
Dave