Ok so what makes me qualified to "instruct" troubleshooting one of these when I have only been at it for a month? We'll over 50 years in the troubleshooting business both electronic and engine. I'll be concentrating on simple tests you can do at home with a minimum of equipment or just observation. This is also a synthesis of reading I have done on here and elsewhere by several experienced persons but the information is not shown completely in one place. This will NOT be a "how to fix software" problem thread at least on my part. Maybe some folks knowledgeable in those areas will add to this and help there. These posts will address control of the power supply at the low voltage level and also the high voltage for firing the tube. My observations will be based on my own machine which is the upgraded 40 watt (actual probably 30 watt) unit with USB, LaserDRW software, LED power indicator panel and the all-in-one power supply. Other machines are similar but use the "knob" rheostat power control and the milli ammeter for power indication.
These machines at least at the entry level are stupid simple and with a little care and knowledge you can understand them. The tube has a gas in it that is excited by a high voltage applied to a terminal at each end of the tube. I don't see how it would matter but they all seem to have the high voltage plus or positive applied to the end farthest from the output tube end and ground is attached to the (beam) output end. You could fire the beam by just turning the high voltage on and off, beam on and beam off (This is what the test switch does. It just turns the beam on and keeps it on until you let go of it). Not very useful except for starting fires and alignment but if you do not have any laser output you will mostly be concerned with the operation at this basic level since you can't laser anything without the "beam"!
.Measuring high voltage with a proper high voltage probe:
The first picture is my what is an apparently "good" tube firing at 40% power. Same with the last picture. Now this one is working fine and was burning a hole in plywood while I was taking the picture. Yours could look like this and not be putting any power out if there is something wrong internally with the mirrors inside the tube or some other problem, but we do have high voltage and it is exciting the gas that is inside the tube. You have to start someplace.
Inside the electronics bay is either an all-in-one power supply or maybe a bunch of different supplies for each voltage but basically you will have a 5 volt DC, a 12 vdc or 24 vdc supply. You also will have an approximately 15-20,000 volt power supply. This entry tonight will be about the high voltage supply. The purpose of this supply is to excite or fire the gasses inside the CO2 tube. This generates the invisible beam that we use for lasering. This light inside the tube is NOT the laser beam. Apparently the supply has to first fire the laser at about a 10-20% higher voltage and then it drops to the running voltage until it turns off. In middle "meter" picture I am holding the camera while also holding the probe on the end of the wire that's exposed by the connection to the tube. No voltage is showing because I can't fire, hold the probe, and hold the meter all at the same time. When I did fire it at 40% power the meter "kicked" up and then fell back to about 10,000 volts measured. The meter is a Heathkit IM-5210 test probe. The ground wire side of the meter is connected to the ground post on the rear of the cabinet.
A word about safety: It's a difficult thing to explain all the ins and outs of high voltage but it can travel along even non conductors and over dirty insulators so be very respectful. I cleaned the body and fins of my meter with a clean dry rag before running my test. The bird-on-the-wire shows us that it's perfectly safe to touch a hot wire if there is no path back to the origin of the voltage. In this case that means back to ground! Unfortunately for 20,000 volts that can be a short distance in air, through the soles of your shoes, concrete, wood floor, the laser metal case, just about anything except a couple inches of clean dry plastic or glass. SOOO. Don't get any part of your body between the high voltage in these machines and ground!
Let's get right to it in this first installment with the scariest and most dangerous part! How do you avoid grounding yourself and making a complete circuit through your body and test the high voltage? First remove all loose clothing off of yourself, remove rings, ear rings, chains or other garbage bling that can dangle or conduct and get them away from the work/test area. Now step onto a clean dry 5 gallon plastic bucket that has been inverted so you can stand on the bottom of it (If your fat get someone else to do this part). Make sure of your footing and don't allow any movement while you are doing any of this to get any part of you closer than a foot to any ground including the laser cabinet, the wall behind you etc. You will insure that a helper pushes any test buttons etc at your verbal direction so you holding the test instrument have only one job to do and you don't have to move while taking the measurement. In the middle picture I am making the high voltage measurement with a HIGH VOLTAGE METER! Not some standard voltmeter which besides electrocuting you destroys itself in the spectacular arc!. Are you completely away from anything except the DRY,CLEAN, plastic bucket your standing on? OK your probably safe and this will be just another day you can tell your grandkids about.: While touching the exposed wire on the high voltage end of the tube with the test probe, have your assistant fire the test button and you should read 10-15,000 volts. If you do we can have a 99% (never believe 100% with troubleshooting) confidence the power supply is operating correctly and incidentally the ."test" button and it's control circuitry is fine. If you don't see any voltage or it's really low during this test examine the tube and so forth for carbon tracks, check where the wire comes into the tube bay from the electronics compartment. I said "look" not touch. Shut everything off and with a shorting wire bleed any remaining voltage from the tube high voltage connection to ground. Wait a minute and do it again. If the high voltage was close to correct but the tube didn't light up inside it's a fair bet the tube is dead and requires replacement. If you have no voltage use your eyes to make sure there are no shorts (touching or even close) to ground along the high voltage wire.
Ok you don't have the fancy meter? Well I would suggest getting one but I have come up with another way to "barnyard" test for high voltage: I call it the "Lucius Gale
test": Find a Styrofoam packing peanut. Get a dry piece of cotton thread a foot or so long. Tie one end of the thread to the packing peanut and leave about an 8 inch tail of thread to hold onto. While firing the laser with the test button, bring the packing peanut within about 2 " from the insulated high voltage lead and a little lower than the lead so it can swing in a arc to the wire. At 40% power mine causes the packing peanut to swing solidly over and stick to the wire. It only barely deflects it at 10% power. Not really a very conclusive test but I think if the test is successful you have enough high voltage to fire the tube and your supply is at least "adequate". This does not say anything about power level but just a rough test with things on hand. No deflection would mean no high voltage and barring a shorted wire would point you in the direction of the power supply output or the control circuitry.
In my next installment we will examine the power supply control system. Don't order anything yet!
Does this topic seem useful to anyone? To basic? To complicated?? Incorrect in some way? Also one of the threads I saw mentioned a spark gap test. I don't really like that because it allows the voltage to vary up and down as the arc forms all over the place possibly causing an arc to start a carbon track internal inside the power supply high voltage transformer possibly damaging it immediately or in the future, but maybe not. If anyone has actually performed that test maybe you could describe it in detail. I notice the manufacturers recommend a test with a resistive load and if we had something like that it would also be a very good test.