LS6090 laser problem

[phil2simmons]

Hi all

Our school laser has suddenly lost most of its power, just at exam time. It even has trouble cutting through 380grm card on full power.
I initially cleaned the lenses and checked mirror alignment but there is no change. I did notice when checking mirror 1 (nearest the tube) that this did not give the usual crisp burn mark. This time it was an oval shaped browning of the surface. This suggests to me that there is something wrong with the tube, so I checked the connections at each end and these seem to be OK. I have never been happy with these connections though as they are just a loose push on fit similar to a tv aeriel but not as secure, but I assume they are like that for a reason? One of these did drop off once and reduced cutting performance.

Any helpful ideas of what to do next would be appreciated. I am wondering if it is the tube that needs replacing although the machine has only run about 100 hrs. since it was installed last summer.
Thanks
Phil

[Spooky]

Hiya Phil,

There are a few things it could be but let's rule out the simple one's first

At the exit end of the tube is a focussing lens, ensure that is clean first. If there is any muck on that it will cause the beam to diverge and spread reducing the effective power (90% of a beams power is in the outside 10% of the actual beam).

At the opposite end of the tube is a mirror, check for any burning or signs of heat in the area around that and any signs of any air bubbles in that end of the tube (the small glass chamber right at the very end is the usual culprit).

Alignment you seem to have covered but always worth a check at the final mirror as mine went out yesterday on a machine only 5 days old. It can happen when a machine "settles" or gets bumped or moved.

Water temperature, heat reduces power by a HUGE amount, what temp is your machine running at? (A fish tank thermometer in the water tub is great) anything over 25 degrees and your losing efficiency of the tube hence cutting power (lower temperature water = lower resistance in the tube = more power).

Any bangs, cracks or pops? When a tube dies it usually makes quite a noise (I don't think we are there yet)

Power supply is very unlikely, yes they do die but it tends to be more of "It works" or "It doesn't work" with PSU's,there doesn't seem to be a lot of middle ground. If you do suspect PSU please please DON'T do anything with it, the amps are very low but the voltage even on a 40 watt tube is in the 22KVa range and WILL kill you if you get a blast across your chest.The spark will jump 2 to 4 inches as well across free airspace too....

Connection wise , I use crocodile clips and they provide a good join, the trodes are titanium allow so don't solder very well but always worth looking to see if they are arcing or burned. (If you have had previous arcing problems that can damage a tube, even one with less than 10 minutes life on it)

At the minute I'm leaning towards

1:Dirty tube lens
2:Leaking connection at the electrodes
3:Previous tube damage from arcing
4:Bubbles having damaged the tube mirror

But no necessarily in that order.

Let us know what you find Phil and if no luck I'll see what else I can come up with.

If you get really stuck with something I'm on 07709066493 pretty much 24/7

best wishes

Dave

[phil2simmons]

Hi Dave

Thanks for the response.
Could you please clarify your first 2 paragraphs? You say there is a focussing lens at the exit end of the tube and then in para 2 'at the opposite end of the tube is a mirror'. I thought the mirror was at the exit end of the tube. The only focussing lens I know of is in the cone in the travelling carriage.

I think I have a lack of power at the first mirror after the tube. With a piece of card over that mirror it burns an oval shape about 3mm x 2mm instead of the usual 0.5mm diameter burn. Due to this I feel it is nothing to do with the other mirrors, hence my concern regarding the tube.

Our water temp may be high, while I was checking the machine I did notice the water was warm. My son works in a fish retailer so I will get him to bring home a thermometer.

No bangs, cracks or pops have been reported to me or my head of department. Mind you the kids probably wouldn't report it anyway, but most of the time there is an adult in attendance.

Unfortunately I will not be able to look at the machine again until Tuesday, so will report back then.

Must go as our IT dept. are about to shut down our system.

Thanks

Phil

[Spooky]

Hiya Phil,

Right at the end of the tube is a lens (it's part of the tube), this reduces the beam from 12mm or so inside the tube to 1 - 3mm as it exits the tube. This lens can get dirty if your extraction has been blocked or turned off, the usual cotton bud (very gently) will remove any much and ensure you don't get divergence.

At the other end is an internal mirror, this bounces the beam back and forth inside the tube picking up power on the way, again this is integral to the tube, on occasion bubbles will form in the mirror end of the tube causing heat and cracking of that mirror,this will usually result in a weird shaped beam on exit from the tube. From what you have said I have a suspicion that this mirror may have cracked due to overheating caused by bubbles.

This is the single biggest cause of tube death over anything else.
On every start up this small chamber should be checked for bubbles after running from cold for 10 minutes, pinching and releasing the water supply tube will often clear them if they occur. Sadly the internal water flow meter won't detect bubbles as water is still flowing, what you end up with is a hot spot that will effectively kill a tube in around 10 minutes of use.

Overall I'd guess that it's either the tube mirror or damage to the tube from arcing once the tube lens has been cleaned and checked.

Failing a first hand look at it I'd be preparing to replace a tube from where I'm sat.

best wishes

Dave

[Pedro_Hernandez]

Hi Phil

I'm afraid I would have to concur with the Spookmeister sounds like the tooby, the oval shaped burn mark at an extended amount of time on the first mirror is exactly the same symptoms our 1290 at School exhibited when it failed.

Only a visit from the Mr Nice Guy Chris from HPC with a sexy new glass thingy ma jing sorted it out !. Unfortunately the first one met a premature end due to abuse , the use of hard tap water and a poor maintenance regime meant it lasted less than a 200 hrs from instalation. I'm glad I joined when I did or the poor thing would be in a sorry old state by now. It realy cant be hit home hard enough about bubbles in the tube, ignore at your peril !.

I still have the old tube in a box at work and intend to mount it on the wall for posterity resembling a stuffed or simulated plaster model of an extinct creature like the Dodo, why oh why couldnt they just of eaten Chicken.

Regards

Peter

[phil2simmons]

Hi Dave

We have checked the mirror at the end of the tube (the one housed within the exit of the tube) and this was spotless. We did note that there are bubbles where a silver coloured insert is fitted into the tube (about 40mm from the end of the tube). It looks as though this insert is glued into place and that there are bubbles within the glue because these bubbles will not move. I could be wrong and they may be stubborn air bubbles?

At the other end, where the water enters, there was a bubble in the small chamber, the only way we could get rid of this was to removed the tube, tip it up and pinch the water inlet tube. At this end, inside the tube, it looks as though there is a brass coloured sleeve but nothing dark as though anything is burned.

Is there any other way to tell if the tube has gone kaput?

Phil

[Mr Bea]

Hi Phil
I had a problem where the water overheated (went above 25c) and this caused either the mirror to warp or the glue holding it to soften and therefore allow the mirror to move. Don't know if that helps at all or just adds to the problem.......sorry but thought you might like to know.

Thanks
Tony

[Spooky]

Bubbles....

Not good, I would suggest that either the tube mirror is cracked or the tube lens is cracked, at the moment I am leaning towards the mirror being knackered due to heat cracking from the bubbles

It really is critical on every laser start up to ensure there are no bubbles in either of these chambers, heat build up can take 10 seconds to destroy a mirror

Checking the lens can be done by looking at the tube end where the beam exits as you have done but in reality there is no easy way to see if the Mirror is cracked (it can be a tiny almost microscopic crack on the surface and still kill the tube)

I can't say with 100% certainty as I haven't actually seem the item itself but I'd be looking at a new tube Phil based on the out of round beam at the exit end and the bubbles in the mirror end.

When fitting a new tube, get it just and just pinch tight, then rotate it with the water running to get out the last of the bubbles.
On start up each day run the water for 15 minutes then have a look for bubbles.

New tube time in all likelyhood my friend

best wishes

Dave

[phil2simmons]

I think it must be time to bite the bullet and get a new tube. Will probably get a timer to start the pump automatically and leave it running all day and check for bubbles more regularly. Will monitor water temp as well.

Thanks for all your help.

Phil

[johnb80]

I leave our pump running 24/7, make sure the return pipe is under water and then no air can get into the system.

J