JDSU 25ML Argon Help

[Mosc007]

I have been doing some testing with the Igniter board while I am at work tonight.

Connected a 150 VDC supply to the Ignitor board using a 110v 25w lamp in series in case of a fault.

Connected the output to a Large CFL tube using a 68k 10w resistor to limit the current. I don't want the CLF tube to actualy ignite and try to run.

Anyway, Activating the Igniter Circuit thru the Opto Couple the Igniter board seems ok. I am getting a white flash inside the CLF tube about 2 times a second. Just in case I replaced the 500 pF 6 KV cap with a 220 pF 6.4 KV cap. Made no difference. Same white flash in the CLF tube. I put the 500 pF 6 KV one back in.

The Flash in the CFL tube is of low output. It is visible in a highly lit factory workshop though. I suppose that would be ok. The Ignitor board seems fine. The Main Trigger Cap is new. It's firing ok. Trigger Cap charges up to the full 150 VDC then its dumped into the Tranny.

What I will try next is to use a 150 VDC supply at home and do the same test with the Argon Tube. Leaving the 68 K in series so the Tube can't turn on fully.

When I tested the Tube last night with the HeNe supply their was a Purple glow inside the Tube. It was pretty low brighness though. With a very dark room I could see it. But their is no way I would have seen it with the Filament glowing.

 

[Mosc007]

I am pretty sure the igniter is working correctly.

I was almost certain the power supply is working.

To confirm the power supply is working I put my oscilloscope on the Anode voltage at the terminals inside the power supply.

If I understand what is happening it looks like this Tube won't maintain ionisation unless the ignitor voltage is present. Watching the waveform on the Anode voltage while it's trying to ignite their is a small voltage drop each time the igniter ticks. But only for a very short time then the voltage goes back up to 170 volts. The amount of voltage drop varies and the time it drops also varies. Sometimes 1ms and sometimes 10ms. But it doesn't stay ionised and the voltage goes back to 170v. At no time the voltage drops even close to the 105v needed to maintain the ionisation. Drops maybe 5-30 volts below the peak of 170 volts.

I think this tube has been abused. Ths filament voltage has been well over spec and I suspect he was running the current well over the recommended max of 8 amps. I dont know if it's normal but the center of the tube has what looks like heat marks on it.

I don't think it will ever lase again. Unless I am missing something obvious. Possibly Cathode failure from way over spec filament voltage and over spec Anode current...


Charles

 

[diachi]

I am pretty sure the igniter is working correctly.

I was almost certain the power supply is working.

To confirm the power supply is working I put my oscilloscope on the Anode voltage at the terminals inside the power supply.

If I understand what is happening it looks like this Tube won't maintain ionisation unless the ignitor voltage is present. Watching the waveform on the Anode voltage while it's trying to ignite their is a small voltage drop each time the igniter ticks. But only for a very short time then the voltage goes back up to 170 volts. The amount of voltage drop varies and the time it drops also varies. Sometimes 1ms and sometimes 10ms. But it doesn't stay ionised and the voltage goes back to 170v. At no time the voltage drops even close to the 105v needed to maintain the ionisation. Drops maybe 5-30 volts below the peak of 170 volts.

I think this tube has been abused. Ths filament voltage has been well over spec and I suspect he was running the current well over the recommended max of 8 amps. I dont know if it's normal but the center of the tube has what looks like heat marks on it.

I don't think it will ever lase again. Unless I am missing something obvious. Possibly Cathode failure from way over spec filament voltage and over spec Anode current...


Charles

I'd be interested in seeing pictures of the "heat marks" if you can.

Could be a cooked tube, I still find it odd that it'd just die while running like that though. Of course, it could have been on it's way out anyway and it just couldn't maintain ionization at 4A, died as a result and refused to start again. A damaged cathode from over voltage and long runs with excessive tube current could certainly cause issues. Had it been sitting for a long time without running before you got it? Or has it been on for a long time at high currents? There should be an hour meter in the head, that'll at least tell you hours on tube.

Could pick up another tube for cheap and swap them over, that'd confirm it. There's one here, tested/working (seems to be making good power too) for $75 + shipping:

Bright Blue Uniphase 488nm Argon Laser Tube Head Nice Beam Has Issues | eBay

EDIT: ACTUALLY, maybe avoid that, description says it has a broken filament.

 

[Mosc007]

I did some reading about cathode failure. This tube does show signs of what has happened. It can stop working suddenly when their is no clean part of the cathode left it simply goes out. It did ignite at full current when it arrived. He had the Light Mode Pot set to max, I never checked anything when I turned it on the first time. It did Ignite First tick. The Supply was probably outputting it's max current. Could be 12 Amps with this supply. That Zener was in the area of the anode output. I think its some sort of protection circuit. It might have been overloaded. It Ignited first tick a second time. The smell was still their so I turned it off. Repaired the Blown Zener. It then Ignited first tick but the beam was a very low output. After 30 seconds the beam went out and has never come back on again.

Might be interested in that tube. Should be no problem running with this supply. What Tube is it ?... Specs. I saw the one on Ebay with the broken filament.


Photo of what looks like a burn mark in the center of the tube.

 

[paul1598419]

That does look like this tube has had a hard life at one time. Still, I'm with diachi in that if it lased the first time, it is unlikely to be a tube failure at this point. It isn't impossible that the tube has failed, just unlikely.

 

[Mosc007]

I am open to suggestions as to what I can try. The Anode voltage tests ok. The Filament voltage tests ok. The hot colour of the filament looks ok. The Igniter tests ok. The gas tests ok with HeNe supply. It just won't maintain ionization at the correct anode voltage. I don't know what to try next...

 

[ultimatekaiser]

Well if the filament is dead, it'd read open when disconnected from the supply...I'm not sure what to tell you myself.

 

[paul1598419]

You said you could see the glow from the filament, right? So, there is no need to measure it with an ohmmeter. I'd recommend the tube that diachi gave a link to, but it has seen a very hard life and has issues of its own. Probably you could talk him down from $75.00 to maybe $45.00, so with shipping it would be less than $100.00. ultimatekaiser is my go to guy on argons. If he has no ideas, then I don't know what to tell you.

 

[Mosc007]

Well if the filament is dead, it'd read open when disconnected from the supply...I'm not sure what to tell you myself.

The filament heater is working. But a dead cathode doesn't always mean it's not glowing. In order for the cathode to emit electrons it has a coating on the tungsten. When that coating wears out or becomes blackened it won't emit electrons at the correct rate.

 

[Mosc007]

You said you could see the glow from the filament, right? So, there is no need to measure it with an ohmmeter. I'd recommend the tube that diachi gave a link to, but it has seen a very hard life and has issues of its own. Probably you could talk him down from $75.00 to maybe $45.00, so with shipping it would be less than $100.00. ultimatekaiser is my go to guy on argons. If he has no ideas, then I don't know what to tell you.

Yep, Filament glows fine. But the coating may be worn or blackened.

This tube is kinda like it's high pressure but that doesn't make sense. It did ignite first tick on 3 occasions until it went out. Also, according to Sam's faq's the cyonics tubes can be left on the shelf without being used for a long time and they fire up fine.

 

[paul1598419]

It is unlikely that a tube that lased for you, what, three times would have a cathode failure now. It would be great if you could eliminate the tube by subbing another for it. The tube looks like it has had a hard life, but that doesn't mean it won't work now, especially since it did just a couple days ago.

 

[Mosc007]

Cathode failure occurs slowly over time until one day it cant pass enough current to hold ionization. That appears what happened the last time it started up. Low power beam for 30 seconds then went out. But, it can occur very rapidly if to much Anode current is passed thru the Tube. I have no idea how long it's been running with 3.5 volts on the filament. That also speeds up cathode decay. And it was run at high current.

Looking at the Anode voltage on my CRO the tube is trying to start. But 170 volts won't pass enough current to maintain ionization. Being in Aus their is not much of this equipment around. And shipping costs from the states is a killer.

What I might do is setup a higher voltage supply. Charge some caps up to 250 volts and trigger the tube. If it won't hold an ionization at that voltage then their is no hope for it.

 

[paul1598419]

I wish you luck with your next trial. It is difficult to try to troubleshoot something over the internet. If my argon were having this problem I might go a different way, but I would have the advantage of having it in front of me and plenty of test equipment to work with.

 

[Mosc007]

I wish you luck with your next trial. It is difficult to try to troubleshoot something over the internet. If my argon were having this problem I might go a different way, but I would have the advantage of having it in front of me and plenty of test equipment to work with.

It would have been nice to have another tube or power supply to confirm my tests.

If you have any suggestions on what I could do next it will be much appreciated.

 

[diachi]

It would have been nice to have another tube or power supply to confirm my tests.

If you have any suggestions on what I could do next it will be much appreciated.

Could try posting a thread over on Photonlexicon. Don't think there's anyone on these forums that knows more about gas lasers than Mixedgas on PL.

I'll keep an eye out for tubes for you...

Edit:

There's a bunch of cheap (although untested) heads on eBay just now. There may be others, doesn't hurt to check!

http://www.ebay.ca/itm/JDS-Uniphase...071268?hash=item2ca58d7164:g:F2gAAOSwwE5WZ5Xx

http://www.ebay.ca/itm/JDS-Uniphase...735636?hash=item1a294805d4:g:vmgAAOSw03lY5vXm

http://www.ebay.ca/itm/JDS-UNIPHASE...249449?hash=item3d3486b8e9:g:5cwAAOSwhlZYtW-n

 

[Mosc007]

Thanks Diachi.

I check Ebay regular but for some reason those from Ebay.ca dont show up. Might consider one of those so I at least have something, I woukd prefer a mulitilne though. Those prices are better than the heads I have been finding. Shipping to aus is expensive though. I posted a message on photolexicon.

Update. I just ordered the bottom one you linked to. Looks in good condition. Shipping is almost double the price of the head. Hopefully it will be ok.