HeCd startup issues, could use some help! *video included*

[GooeyGus]

Hey Guys,
Today I finally got my liconix 4240 HeCd laser. It was actually in one piece when I got it!! And gas in tact!! This is the first glass tube laser I've gotten that didn't break in transit. I'm 1 for 4 now

Ok... the details: This tube came packed in it's original packaging. The hour meter reads 3700 (exactly 3700!). The meter is digital, so I'm not sure if it's 3,700hrs or if it's 370.0hrs. Anyway, the glass inside looks pristine, still shiney. No shitty buildup or anything like that. This tube is a 'dual discharge' tube, I guess meaning that it has discharge on either end. One end lights up instantly and maintains just fine. The other end I am having some troubles with. It flashes while it is trying to start, doesn't start, and then the PSU quits trying. Now, when I shot the video this is all the info I had. Upon further investigation I found that the HV wire that goes to that end of the tube is actually arcing, and I'm guessing that is what is causing the issue. It will light for a second or two, then you hear a little *pop* (you can hear it in the video, at the time I didn't know what it was) and the discharge stops on that end. I'm guessing I will need to get a new HV cable for this end of the tube, any suggestions on where to pick one up??

Here is the video, see if you agree with my theory

http://s269.photobucket.com/albums/j...t=000_1126.flv

I'm sure it is just an issue with the HV wire needing to be replaced, as everything else on this head and PSU looks amazing and the discharge on the other end has absolutely no problem.

Let me know what you think.

[Diachi]

Why don't you just put a metal rod in place of the wire, just to test if it works, bit of copper pipe or something ?

Just to save you buying stuff if that's not the problem.

-Adam

[heruursciences]

Replace the HV wiring where it arced out, then try testing the cathode filament on the side with the firing issues. I believe they made these tubes with an auxiliary filament, so if the main filament is open you can go to the reserve filament. If the filament is OK you need to recondition the cathode by heating it to a bright yellow glow. Try zapping the tube with an Oudin coil as well as it may be that some cadmium condensed in the bore causing it to short parts of the tube and kick out.

FWIW, The yellow glow and sustained discharge in the working part of the tube is a good sign and means your tube is more than likely healthy.

[GooeyGus]

Replace the HV wiring where it arced out, then try testing the cathode filament on the side with the firing issues. I believe they made these tubes with an auxiliary filament, so if the main filament is open you can go to the reserve filament. If the filament is OK you need to recondition the cathode by heating it to a bright yellow glow. Try zapping the tube with an Oudin coil as well as it may be that some cadmium condensed in the bore causing it to short parts of the tube and kick out.

FWIW, The yellow glow and sustained discharge in the working part of the tube is a good sign and means your tube is more than likely healthy.

I removed the metal cover for the HV terminals and it is now no longer arcing, but still no maintained discharge. There are three terminals that I think are all part of a ballast resistor. two are taken up by the HV wires, the third is just open. It was the open terminal that was arcing. As far as I know, these liconix tubes dont use a filament like the omnichrome tubes do, these have a cold cathode design. I'm going to try to switch terminals where the HV is to see what happens. I think it's just a ballast resistor as it says: 3Kohm and then has a wattage value... I think it's 20W. would a dead ballast resistor cause the discharge to fail to maintain?

[heroic]

I'm guessing I will need to get a new HV cable for this end of the tube, any suggestions on where to pick one up??

You can get HV cable off a spool at any decent car parts store- it's what goes to the spark plugs. This stuff is typically rated to 45 kV, so you should be fine. Make sure you get the copper type, not the carbon string type. (Tell them it's to fit a "resistance cap" and they'll understand.)

Failing that, find a TV repair store that repairs on site and they may have short pieces available from dead flyback transformers.

[GooeyGus]

I got it running!!!!

I noticed that the ignition pulse kept going down the helium reservoir rather than the bore of the laser. I had already tried my oudin coil a few times without success at the electrode, but I got it out for one last try. This time I shocked the bore of the tube (right where I wanted to pulse to go) and it instantly maintained!! About 5 minutes later I had some beautiful 442nm light coming out... Here are some pictures.

Not running yet:


The side that did sustain at first:


This is the side that kept flashing. As you can see the bore of the tube is in the center, the electrode to the left and the big helium tank off to the right:


Holy crap I got it to stay lit!!!


Lit, but no lasing..... yet.


success!!!

[DZ]

Wow! Nice job, that looks very nice!

[Laser Ben]

Horray 442nm! Looks nice!

[allthatwhichis]

That's purdy! Need to find a diode that color.

[GooeyGus]

Is there any way to adjust power on these or are they like a HeNe in the sense that you turn it on and that's the output that it's going to stay at?

it's pretty bright, and keeps getting brighter as it burns in, but I was just curious