Omnichrome 532/150T

[Xenonion]

Hello,
This is my first post here. Bought a Omnichrome 532 low hours, and high years (1994) from the auction site we all know and love. The laser arrived in the packaging expected for what I paid, a piece of foam and a few sheets of newspaper.

Checking Sams Laser FAQ, per the arrival instructions provided in the the ALC 60X/532 maint. section. The heads cathode/anode were checked to see if they were shorted to ground/chassis and they were not. Filament read good also, my complete surprise that this laser head had made it mostly? intact! The head and power supply are very clean inside, and although I didn't expect any alignment to have survived the beating by the post office thought i'd fire it up to see what happens.

After powering up, the filament came on, delay relay tripped in the PSU and head started clicking away. The tube didn't establish any arc, but would flash blue/purple. Well shoot, so I bought a cheap oudin coil from Amazon, to be overnighted.

With the HV coil, the system was powered up again, and a weak HV was applied to the joint near the thermal cutout and the tube ignited! No laser output, but that was expected. Now the laser stayed on with cooling to try to burn in the tube for maybe 2 minutes. CLICK! The 20 amp fuse breaker tripped at the fuse board. Reset the breaker and reignited the tube, however I had to leave and couldn't leave the laser on (). I haven't been able to get the tube to ignite since (couple of days of attempts). So which direction from here.

A few more details:

1. Voltage across tube before ignitor starts ~145-150 VDC (slowly rising)
2. Ignitor boost voltage between 400-500vdc
3. Tested optical feedback. 2 9V batteries, measured light output from sensor section, at darkness reads 0.00Vdc, with flashlight on solar cell ~3.3Vdc. Seems to be functioning.
4. Disconnected the ignitor caps 10 µF at 400V, basic capacitance test, gives 10.0 and 9.99 µFs for both. They seem fine, however I don't have an LCR to test leakage.

Couple of thoughts:
1. The current across the tube wasn't measured when it was lit, and I haven't been able to light it since to get any current data. I'm not sure if the PSU is functioning perfectly, but expect it is in good condition. Even though the breaker blew, it tripped because the heating system came on at the same time as the Laser was running.

2.Based on the documents available in the FAQ, the remote connector can put the laser in current regulation mode. However, this doesn't override the light feedback if the light feedback is demanding higher current? I've moved the light feedback wiper from the laser head to the power supply pot, by removing the remote pins from 3-4 to 2-3. But did not see any change in head behavior. How does one put the laser in current regulation mode? Based on the connector, a potentiometer (100k?) can be connected between pins 9(5.1V ref)-1(common)-6(Wiper, current Drive)

3.What is the typical ignitor behavior? The ignitor lights (Ticks) once every 3 seconds or so, which seems like a long time between pulses. The voltage climbs slowly on the HV capacitors before the pulse occurs.

Thank you for any direction yall can lend. I'm not willing to give up on this tube yet.

Mark

[buffo]

I'll defer to Steve Roberts, as he's the acknowledged expert when it comes to all things ion (he wrote most of the Ion Laser section of Sam's Laser FAQ, after all), but based upon my admittedly limited knowledge of the 60X / 532 tubes, I think your unit is *very* high pressure.

Normal tube voltage should be around 110 volts for a tube that size, but yours is way up at 150 volts. Not good. Given that the power supply runs on 120VAC, you are flirting with the maximum voltage possible from direct rectification of line voltage.

Some people have had success resurrecting old argon tubes by running them on a HeNe power supply for several days to try to bury at least a little gas in the hopes that the pressure would come down enough to allow the main power supply to fire the tube and keep it lit. Trouble is, a HeNe supply generates ~ 6 mA, which doesn't create any significant heat. But the main power supply will be running at several amps, even at idle, which most definitely will create heat, and if the tube is already high pressure, this can force the pressure even higher, until it winks out. (Had this exact problem with an HGM-5 I was trying to resurrect back in the day. Alas, I was not successful.)

In theory, if you can maintain an arc down the tube, eventually you'll bury enough gas to bring the pressure down to a reasonable level, at which point you'd be fine so long as you ran the tube periodically to prevent it from going high pressure again. (Of course, this assumes that you don't have a leak.) But given how high your tube voltage is, I suspect you might not be able to save this one. Again though, I'll defer to what Steve has to say...

Either way, best of luck. (And PS: Welcome to PhotonLexicon!)

Adam

[Xenonion]

Hello Adam,

Thank you for the welcome and reply.

Normal tube voltage should be around 110 volts for a tube that size, but yours is way up at 150 volts. Not good. Given that the power supply runs on 120VAC, you are flirting with the maximum voltage possible from direct rectification of line voltage.

Keep in mind that the values I quoted previously are without any plasma established, and likely the powersupply just floating to its limits. So this is really just an unknown but likely the tube is very high pressure.

Some people have had success resurrecting old argon tubes by running them on a HeNe power supply for several days to try to bury at least a little gas in the hopes that the pressure would come down enough to allow the main power supply to fire the tube and keep it lit. Trouble is, a HeNe supply generates ~ 6 mA, which doesn't create any significant heat. But the main power supply will be running at several amps, even at idle, which most definitely will create heat, and if the tube is already high pressure, this can force the pressure even higher, until it winks out. (Had this exact problem with an HGM-5 I was trying to resurrect back in the day. Alas, I was not successful.)

Time to dig out a HeNe PSU and start it running. I'll disconnect the leads to the head from the cathode and remove the ignitor connection. Again I agree, that this will have little effect but at this point, the head is just a highly engineered and amazing looking paperweight/boat anchor. Along similar lines, I'm not opposed to beating this tube up with more barbaric means such as a µwave transformer (isn't sputtering a problem?) or a homebuilt PSU with a boosted operating voltage or something similar (hours of a marx generator running?).

Take Care,
Mark

[mixedgas]

I'm at work and I have a concert laser gig right after work.

Tomorrow b4 I can reply.

Don't do anything yet.

A good tube would be ~ 106.5 drop volts @ 8 amps.

Blowing the breaker tends to mean the MOSFETS, recovery diode, or BUCK cap in the PSU are shorted. Not easy to check with an Ohm Meter.

Steve

[Xenonion]

Hello Steve,
Thank you for any insights you can give.

Although I don't have a differential probe yet, I can test with a scope out of circuit if required.

Keep in mind that after the breaker blew I was able to restart the laser but had to leave and shut the system down.

Though, I'm still interested in the ignitor circuit, and if it is under performing at the very least (pulse every 3 seconds).

Take Care,
Mark

I'm at work and I have a concert laser gig right after work.

Tomorrow b4 I can reply.

Don't do anything yet.

A good tube would be ~ 106.5 drop volts @ 8 amps.

Blowing the breaker tends to mean the MOSFETS, recovery diode, or BUCK cap in the PSU are shorted. Not easy to check with an Ohm Meter.

Steve

[mixedgas]

You need an isolated scope (isolated from POWER HOT, NEUTRAL, AND GROUND) for reading the test points. Which is dangerous as can be.

Send me a PM with a email address and I'll see if I still have the procedures with waveforms to scan in..


Steve

[mixedgas]

You need an isolated scope (isolated from POWER HOT, NEUTRAL, AND GROUND) for reading the test points. Which is dangerous as can be. There is a startup adjustment procedure post repair.

Send me a PM with a email address and I'll see if I still have the procedures with waveforms to scan in..

You need to look at c35, D20, Q8, Q9, c11, c12, c13, the gate drivers / gate clamping on both sides of the gate transformer and D20 as a minimum on the power section.

C35 / D20 failures happened often.

Run in current if you can, till repaired. Oscillation was easy to obtain if your not careful with the adjustments.


https://www.repairfaq.org/sam/150rpsch.gif

https://www.repairfaq.org/sam/150rcsch.pdf

https://www.repairfaq.org/sam/532hsch.pdf

There is a beast called a "noise potentiometer" and loop gain potentiometers that I remember needing careful adjustment.

Steve




Steve

[mixedgas]

Also it never seems to amaze me about the number of bad / overloaded breakers out there. False tripping from a reactive load like this is not uncommon. Toss in a GFCI etc if you have one as a known issue with these. I know the 170 series seems to be a redesign including a power factor correction module and a lot of extra line filters.

GFCI / AFCI do not like Oudin/tesla coils and switching laser PSUs.

Steve

[mixedgas]

Hark! There is hope. Check that the circuits match, but here are most of the waveforms I would have had to scan...

https://www.skywise711.com/lasers/Om...ual/index.html

I quote his opening paragraph and agree:

IMPORTANT SAFETY NOTE: Make sure the test equipment is AC line isolated before working on laser. Use an isolation transformer for the laser power supply. A rating of 5 kW is adequate. The isolation transformer may be removed for final noise measurements, after the scope is removed from the circuit.

[mixedgas]

]Hark! There is hope. Check that the circuits match, but here are most of the waveforms I would have had to scan...

https://www.skywise711.com/lasers/Om...ual/index.html

Edit: Check all the picofuses... They look like 1/8 or 1/4th watt resistors but ARE fuses, before you do anything else.

I quote his opening paragraph and agree:

IMPORTANT SAFETY NOTE: Make sure the test equipment is AC line isolated before working on laser. Use an isolation transformer for the laser power supply. A rating of 5 kW is adequate. The isolation transformer may be removed for final noise measurements, after the scope is removed from the circuit.

[/QUOTE]