Omnichrome 532/150T

[Xenonion]

Hello Steve,
Let me compress these messages into one reply, your comments are in blue.

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.”

The search begins for an isolation transformer. There’s going to be a bit of iron in that transformer, for 5 kW’s. While that goes on, I can familiarize myself with the power supply and component location, looking for anything obviously burned up. Such as checking the picofuses.

MixedGas: “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.”

D20 (MUR1560) and C35 (220 µF/250V) are straightforward, so I’ll get a few of those and Q8 & Q9 if I can find the part number.

The remote connections will be setup to run in current mode being mindful of the possibility of oscillation.

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

At this early stage, I’m staying far way from any loop/PID adjustments. If they need to be adjusted that can happen when the PSU is performing more or less typically.

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.”

The system is running in the shed, with few other things on those outlets. The breakers aren’t required to be the GFCI/AFCI here and I’m glad actually. The GFCI’s are very sensitive like you say to RF and switching PSU’s so I’d rather keep them out. What still bothers me is that after power down by the breaker going out, the laser system was powered back up and reignited fine.

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.”

Excellent, thank you for the links! Indeed, I’ll heed the warnings with these power supplies. Although, relatively comfortable working with lasers, high voltage, and power systems the safety aspects can never be over emphasized..

I’ll take a good look at the fuses before going any further.

Mark

[mixedgas]

1750 Watts calculated.... You might get away with a much smaller isolator.

Also if I remember right, check the anode pins in the cable. If "cooked" they tend to pull away from the CPC connector on the umbilical.

Series 4/5 CPC tools for pin change are out there.

Steve

[Kevint]

Just a comment. Be careful and make sure that tube is lighting down the main central bore and not a gas return path. When the tube light down the main bore the ceramic will glow a unform blue. If it lights down a gas return path the blue will appear to glow on the outer side of the ceramic depending on which of the 6 paths it took.

The inside of the tube viewed by a cross-section has a central 0.040" diameter main bore surrounded by 6ea 0.020" diameter gas return path bores. It is common for older tubes not run much to light down a gas return path and you will see a higher voltage due to the higher current density. If is does light down one of the 6 return path turn it off. if it runs too long it creates a carbon path and then prefers to light down that path all the time.

Due to ion pumping, the Ar gas is pushed to one end of the tube when it is running. The 6 gas return path allows the gas to circulate.

Cross section of the ceramic tube

[mixedgas]

Was there any cure other than anecdotal for "Down the return Bore" ? I know the one guy has a patent on using a Helium, Krypton, Argon mix (8,2,1) for active cleaning of dirty bores during rebuild. I had one or two clean up over the years with a soft discharge at a 20 mA or so, but it was never repeatable.

Steve

[Kevint]

Yes, the addition of another nobel gas was one option, but could reduce laser power or change the tube voltage. Our primary solution was to insert a 0.5" long piece of nickel wire into each end of the gas returns. This significantly helped reduce the likelihood of Ignition down a return. It's a balancing game to create a path of least resistance and maintain proper gas flow. If the returns are too small the tube will not sustain a discharge or extinguish
at higher tube currents which increases gas pumping. Diameter of the bore to the diameter of the gas returns, the number of gas returns to get proper gas balancing, the distance of the gas returns in relation to the main bore, all of these together play a part in minimizing Ignition down a return path and sustaining a stable discharge.