Omnichrome 643 / some issues

[Therion]

Hello forum

this is my very first post here, I've been reading since a couple of month's here however.
As mentioned I've an Omnichrome 643 Ar/Kr Gaslaser (which should be equivalent to the Melles Griot 643 one).

I also posses (since today) a suiting power supply (Melles Griot too),
it is for the 643 head - that's for sure.
The main issue here is that the fan's arent powering up, Im unsure if this is a cable/wiring issue.

I can get the laser to ignite but very shortly after this the procedure collapses and then it ignites again... that resumes until I stop that.
I guess it's mostly due the lacking fan's?

Anyone has experience with the Omnichrome 643?
I've one with two dual fans on the top,
of course I can take some pictures as well.

 

[Meatball]

I don't know if there is a thermal protection built into it or not. Pictures will help, but for now, try and get the fans powered up with an external voltage supply so you know the fans actually work. After that, you can test to see if the laser still cuts the tube current after a few seconds. If it still occurs while fans are actually spinning, you may be able to rule out a thermal protection mode of operation.

Let us know what happens. The Ar+ guy is on the other forum, but we'll see if we can get things narrowed down a bit for you.

 

[Therion]

Hi

Thanks for the response, I can actually tell that I can get two different things going on here.
I've no remote control, but the original test board from Melles Griot (so I dont have to short any pins manually).
In normal mode the situation above happens, the dot I can see is clearly yellow (not white).
However if I do it in standby mode (which seems to exist for testing situations; lower current to the tube) I can get a constant dark blue dot. (I didnt identify the nm)
So the tube is not dead nor broken - that's for sure.
I can also confirm that this laserhead was pulled from an working environment (not by me though) - I'll try what you suggest in the evening.
It is most certain that this head also didnt run a couple of month in a row too.

I must say that Im very new to gaslasers, I do understand the theory behind of course -
I've an working (in good condition) ALC60X head but I never had to tinker with it yet.

I'll attach some pictures of my head just so you can see, as I undertand there are different head models - also one which have an external power connector for the fan's.
I dont have that on mine, the two fan's are sitting (screwed of course) on a top board which can be unscrewed by four screws.
Then you can take the whole top board of and there is a cable from there going inside the laser head.

There is a manufacture label on the other side:
Omnichrome
Model: 643-75RYB
Serial No: 1228
Manufactured: Oct. 1993

The actual power supply Im powering up with is an Melles Griot 400-K06

Edit:
I also have forget some thing to mention, as soon as I turn on the power supply - the laserhead gets AC power as well of course.
At that point I can hear a continuous clicking from inside of the head (not loud though) it sounds more like an electronical element / relais or maybe it has something to do with the hour counter - I dont know if this is usual to this head model.

 

[MarioMaster]

Ticking sounds from an ion laser is usually the igniter circuit that starts the tube, but the power supply almost always has a built in time delay so ticking immediately at power-on makes it seem more probable that it's just the hour meter as you mentioned.

The blue only at idle current makes sense. Argon has higher gain than krypton so you will see only the argon lasing at lower currents.

I would definitely NOT recommend running the laser again until you can get the fans powered up, the tube will be dissipating several hundred watts of power and can damage itself rapidly if the thermal protection isn't 100% on the ball.

That's a sweet laser though, those mixed gas omnis aren't easy to come by.

 

[cheech226]

i have to echo - you've run it too long as it is without cooling, please don't fire it up again until you get the fans going.

 

[Therion]

i have to echo - you've run it too long as it is without cooling, please don't fire it up again until you get the fans going.

I didnt run it that long, just a couple of seconds.
Anyways I want to tell about my progress so far - first I've been in touch with two people on an german forum.
www.LaserFreak.net ? Thema anzeigen - Omnichrome 643 in Betriebnahme
I hope it is okay if I post the link here, it's an german board -
however I've put a lot of photos there too.

To summarize it, I had the fan issue - I figured out that my cable (from the ALC60X) didnt have all pin's - in particular pin 4 is lacking, which seems to be coming from the power supply (probably the fan voltage).
However I now powered the fan's on by an external cable - this worked out greatly.
The fan's are now working... they are running on 200-240 VAC which was suprising enough.

Today I just saw that this somehow doesnt fix my issue, it is in fact the same as before.
In standby mode (I can set this on the melles griot test board) I get a constant beam - but in normal mode it the beam disappears and then it tries to ignite again...

 

[MarioMaster]

If the laser runs continuously in standby but drops out in run mode, it's likely that you are either hitting the overcurrent trip and the psu shuts down to protect the tube, or the tube is high pressure and cannot sustain discharge at higher currents.

See if there is a way to lower the run mode current setpoint.

 

[Therion]

it's likely that you are either hitting the overcurrent trip and the psu shuts down to protect the tube

Cant say that the output was very high, though atm. I dont have a good power meter at hand (I'll get a new one in a couple of days)... it seemed usual to me.
The PSU has an adjust knob for this, of course I've used the lowest possible state.

See if there is a way to lower the run mode current setpoint.

Excuse me, how so? Inside the PSU or at the laserhead?

...or the tube is high pressure and cannot sustain discharge at higher currents.

Interesting it might be possible - would running it long in standby mode fix this issue?

Edit:
I want to add that if in normal mode, I get a yellow (almost gold) dot - no white at all - is that normal?

 

[Therion]

Hi, it's me again...

Im ongoing tinkering with my precious laser...
I ruled out the ignition issue, by setting the Melles Griot test board to current control (rather than light control).
It might be that either the cable or the PSU is not 100% compatible with the Omnichrome.

I also began aligning the mirrors, as they were deadjusted - Im not finished with it yet.
However I noticed that whatever Im doing, with alignment - Im lacking all argon lines...
This is strange - on a pretty high current Im getting a good orange, however if I push it a lil' bit further the beam will disappear and the PSU ignites again (same issue as in the beginning then).

In normal mode, prior adjusting (the green is definitly yellow, cam cant record it):

last result, after adjusting:

 

[MarioMaster]

It's possible that your laser is either krypton only or it has krypton only mirrors, preventing the argon from lasing.

Since you obviously have the krypton lasing, if your laser has argon in it (and whitelight mirrors) then 100% it should be lasing at least 488nm blue by now.

 

[LSRFAQ]

Couple of issues. 643 (krypton/Mixedgas) series supplies sometimes have a small boost transformer in the supply that 543s do not. 643s also sometimes have a ignitor that needs a remote shut off signal that does not come from all Omnichrome supplies. Is the boost transformer (small round thing that looks like a grenade) there?

If it winks out when switched to light from standby, check the +/- 15 volts to the light sampler board in the head, check the light feedback photodiode, check the light sampler op-amp and 2n2222A transistor. Make sure the test board on the remote connector is supplying a few volts to the current or light pin, if its not, there is no "demand" signal and the tube will go out. If there is no light feedback from the head, the psu can go to max amps limit (usually what happens) or hit the trip-out circuit. In some cases, if there is no demand signal on light or the current inputs, its going to go below plasma dropout current.

If the noise gain pot in the psu is set incorrectly, you can have issues as well, but that is NOT something to check just yet. Don't mess with it, you need a isolated HV capable scope to set it, as the PSU internals are at rectified line voltage. As well as the factory procedure book. I have it at home.

643 supplies vs 543 supplies can have some serious differences, and we have some detailed in Sam's FAQ.

I'm betting its a configuration issue, or a problem with the head setup. It would not function at standby if there is a serious problem.

If your not lasing, it will go to Imax in light mode. Imax can make the Krypton based tube oscillate, too. These non-argon tubes barely have enough internal gas return paths for what they need to do, and that can cause oscillation in some cases, at some currents.

Standard Argon style diagnostics rules do not quite apply for these tubes, they are very fussy compared to a stable argon fill. I have not worked on one for 5 years, but I will try to help you.

I don't check LPF very often due to work computer security issues. Ie the boss does not mind PL, but reading LPF at work is crossing the line. If you have further questions please find me on PL. I do not have access to the net at home, I'm never there.
This is a holiday, so may be 4 days before I post again.

Go to PL, do a intro in the lounge, or advanced tech discussion, and I'll find you.

If I was not on the road, odds are I'd have missed this thread.

Steve

 

[Therion]

Hello

I didnt give up yet, though I was quite preoccupied during holidays.
Finally I got the original Melles Griot cable from someone, I'll check out in the evening,
if the results are different.

Thanks for the useful information LSRFAQ.

Go to PL, do a intro in the lounge, or advanced tech discussion, and I'll find you.

Anyone knows what he means, I dont know what forum PL is?

 

[cheech226]

here ya go: Photonlexicon