HGM-20C Argon laser - Powers On - No Beam :-(

[turbohead]

This is a continuation of my previous thread:

http://www.photonlexicon.com/forums/...hase-Converter

I brought home a HGM-20 Argon Laser a couple of days ago.

The laser is connected to a single to three phase rotary converter (10 HP 240 VAC motor), coolant water, foot pedal, and fiber optic wand.

The laser powers on, no interlock errors, and the "Treat" button lights.

I set the control for 1 watt, .2 sec. single pulse.

When I press the foot switch, an alarm sounds (to indicate laser operation) and the "Pulses Delivered" counter sets to "1."

However, there is not output beam :-(

I measured the filament at 4.3VAC.
There is no obvious damage to the laser tube and the Hobbs meter reads 368 hours.

I am operating the laser with the cover off (interlock switch shorted) and when I depress the foot switch, there is no ionization.

I checked the bridge rectifier, and the three lines of 240 AC is being rectified to 320 VDC.

Attached are pictures of the laser interior and the control panel.

Any help or suggestions would be greatly appreciated.

Willie

[dsli_jon]

Good Sir Willie -

Couple thoughts: 1...

...I set the control for 1 watt, .2 sec. single pulse.

..the human blink-reflex is (average) 0.25 sec. so.. a 0.2 sec pulse is pretty-quick. You might try an 'exposure time' of 1-2 seconds or greater.. unless that was a 'typo' and you meant 2 sec..

2. Do you know the tube is gas-intact? A tube can have no 'visible breaks', etc and yet be 'up to air' (which will never lase..) and afaik, those HGM systems are not 'smart enough' to tell you if a tube is up to air.. if all interlocks, etc, are satisfied, the PS will go-ahead and try to do it's 'brutus-job' of slamming current thru the tube.. The 'computer' isn't much 'smarter'..

Do you have a 'neon-tube tester' / tesla-coil? You can usually buy one / rent one from a local sign-shop that does neon, and test for 'tube-integrity'.. Let me know this first, then we can discuss 'how to', w/o blowing holes in your knuckles...

3. IF the tube is-proven gas-intact (or you already-know it's good..) then I'd suggest it's out of alignment.. either the back-plate (usually the Vertical-adjustment 'walks' out..) is out, or something else has wonked.. ie: You might also *carefully* look down the length of the bore (HR-side only..) thru the HR (Rear) and see if you can see if there's any 'cathode sag'.. That can also kill output.. it's rare to happen, but.. these lasers are pretty-old, and if you don't know the 'health' of the cath, it's a 'legitimate question' to ask / investigate..

Lettuce know.
chers..
j

[turbohead]

Do you have a 'neon-tube tester' / tesla-coil? You can usually buy one / rent one from a local sign-shop that does neon, and test for 'tube-integrity'.. Let me know this first, then we can discuss 'how to', w/o blowing holes in your knuckles...

I do have a portable Oudin coil (neon tube tester). The argon tube is several feet long. When I apply high voltage to one end of the tube, where glass is visible, there does not appear to be ionization. I am thinking this may be due to the length of the tube. I am hoping the tube is intact given that it only has 300 hours. On the other hand, there are indications that the laser was last serviced in 1988.

Please let me know if there is a better way to test for tube-integrity.

[Vidal Wolf]

Be careful when zapping your tube with the coil. The discharge can punch a hole thru the glass.I put a glass test tube or a glass plate from a picture frame over the electrode tip to hopefully prevent any damage to the glass stem. Might be better ways, I dunno. =)
Awesome score on the HGM-20 btw! =)
Also, on the output fiber chuck, If i remember, there is a hole for a pin that will open a mechanical shutter. if you have the fiber, try installing it and see if you get anything. I had an HGM 5 that needed the fiber output assembly put into the laser ( I think )

[dsli_jon]

...Please let me know if there is a better way to test for tube-integrity.

Typically, with a laser where the head / psu are 'independant', and connected via an umbilical, you'd hit-up the glass-stem (not too-close to the brewster-window; covered on yours..) while the umbilical was *disconnected* from the PSU, but ideally 'touching' ground (literally, the connector-shell to the ground...) - you could also touch the 'cathode-stems', but make solid-contact (..so-as not to 'arc' to them..)..

..in your-sys' case, looks like you can disconnect the anode / cathode, here: http://www.photonlexicon.com/forums/...7&d=1388099434 - looks to-me (..haven't been under the hood of a -20 in awhile.. and - literally - alligator-clip another wire from either end, to the earth (ground).. Then, you will be 'isolated' from the psu, and not running thru it, and should - should - be able to get the tube to 'lite'.. IF you just-can't - with one of those ends running-direct to the earth..... Not much hope for the tube-integrity, I'd say.. :/ If you DO 'get lite', then you can re-connect, run the sys on 'as-continuous-mode' as you can.. and you can move-on to 'alignment' or other possible-issues.

Steve (mixedgas) here in the forum may have some other '-20-wisdom' for you, but.. it really shouldn't be that-difficult to get some 'response', especially if your coil is 110V-powered (vs 'battery', etc..) since those usually will have well-more than enough 'kick' to get some response out of most-any good-tube..

I gotta bug, for now..
ciao..
j

PS - (just-now seeing Nates' post..) Yes, be-sure that you've got the shutter open.. Sounds like you've got that 'interlock' defeated (or it would typically not 'fire' / would throw an i-lock error..), but...if you've defeated the interlock - and are still 'shuttered', well.. not much lite will come-out..

[buffo]

Did you remember to defeat the fiber-launch interlock? From the pictures you posted, it appears you didn't.

Cut the tip off a Bic pen cap and shove it in the fiber connector (cut end first). That will satisfy the interlock. Then try it again.

Adam

[turbohead]

Thank you for your replies.

I applied the Oudin coil per the instructions above and started to strongly suspect a dead tube. After a much closer examination, I found a hairline crack at the bottom of the tube where it meets the brass sleeve on the mirror mount. Of course, this is a huge disappointment.

Does anyone know where I can get a used replacement HGM-20 tube?

There is a HGM-8 tube listed on ebay (eBay item number:130925828591). Would it be feasible to operate a HGM-8 tube on this HGM-20 frame?

[mixedgas]

I'm getting on a airplane in 15 minutes. I'll PM you in the morning where to get your tube. I have a friend with a warehouse of them. The 8 is a shortened 20, but you need to limit the tube current. Don't play the argon lottery, too many of them out there are dead.

Steve

[turbohead]

Did you remember to defeat the fiber-launch interlock? From the pictures you posted, it appears you didn't.

I failed to provide a picture with the fiber wand installed which satisfies the interlock.

The front panel has a knob to adjust an aiming beam. When the laser is powered-on, no aiming beam is present. Even though the tube is "up for air," I would expect there to be an aiming beam present. Inside the case, I am not able to determine where the aiming beam would be coming from since a separate He-Ne laser does not appear to be present.

Do you know where the aiming beam comes from? Is it a laser diode? Shouldn't the aiming beam be on when all interlocks are satisfied?

[turbohead]

I'm getting on a airplane in 15 minutes. I'll PM you in the morning where to get your tube. I have a friend with a warehouse of them.

Hi Steve,

Can you please send a PM with the contact information for your friend? Thanks!

Willie