Introduction: How to Test and Set a Chinese (China) Made CO2 Laser Power Supply to Get Long Life From Your CO2 Laser Tube for Your Laser Engraving and Laser Cutting Machine System

Picture of How to Test and Set a Chinese (China) Made CO2 Laser Power Supply to Get Long Life From Your CO2 Laser Tube for Your Laser Engraving and Laser Cutting Machine System

Be safe when performing this project.


The high voltage laser power supply settings can greatly affect the lifetime of the CO2 glass laser tube.  A setting above 30 mA will, in almost all cases, greatly diminish the operational life (changing an expected life of several years to months).  Even though the laser tubes are ranked in months, such as the 60 watt tubes, I have had customers use them for years before they finally loose power.

More recently, the higher power CO2 glass laser tubes, above 80 watts, and certainly 100, 130, 150, and 180 watts have been more inclined to have shortened lives because the power supply is improperly set.  For example, I had an unscrupulous seller who sold me a 150 watt laser with a power supply set at 34 mA.  My Mahoney laser power probe measured 145 watts.  Then, I contacted the seller because my multimeter read 34 mA.  His engineer said the power supply should be set to 30 mA for full warranty on the tube.  After setting to 30 mA, I measured the laser output power and got 129 watts.  Then, I contacted the company and returned the laser because the seller had actually sold me a 130 watt laser with a 150 watt price tag.

Whatever your reason for checking the power supply current, the steps are provided to demonstrate a safe manner to take a reading then take action to remedy.

Step 1: Do Not Touch the Red Wire.

Picture of Do Not Touch the Red Wire.

1. Power off laser machine
2. Wait ten minutes. this is the time for the power supply to drain power from its electrical capacitors. 
3. Setup as shown in photos below.  You will need to purchase and use two sets of wires.  We recommend a black wire with aligator clips on each end and a red wire with aligator clips on each end.  These wires should be available at radio shack.

          A. See the power supply wire connection.  Do not touch the red wire.  It has extremely high voltage that is lethal.

          B.  See the thin wire.  It is colored blue, or black, or green as shown.

Step 2: Insert Meter Wires to Measure Current (mA)

Picture of Insert Meter Wires to Measure Current (mA)

C. See the meter below as an example meter.  Some meters are slightly different, so adjust instructions as needed.  Set meter to read current at mA.  Set meter to read DC current.  Insert red cable of meter into meter connection for current (labeled mA, or micro A, or A).

Step 3: The Meter Reading Should Show the Proper Units (mA) and a Zero Value

Picture of The Meter Reading Should Show the Proper Units (mA) and a Zero Value

Step 4: D. Disconnect Thin Wire (colored Blue or Black or Green) From the Laser.

Picture of D. Disconnect Thin Wire (colored Blue or Black or Green) From the Laser.

Step 5: E. Connect Your Wire to the Laser (aligator Clip Is Useful on Return Wire).

Picture of E. Connect Your Wire to the Laser (aligator Clip Is Useful on Return Wire).

Step 6: F. Connect Your New Wire to Meter Red Wire. Use an Electrical Insulator, Like the Wood Block Shown, to Support the Wire at the Connection.

Picture of F. Connect Your New Wire to Meter Red Wire. Use an Electrical Insulator, Like the Wood Block Shown, to Support the Wire at the Connection.

Step 7: See the Solid Electrical Connection. See Its Location, in the Center of the Wood Insulator Plank.

Picture of See the Solid Electrical Connection. See Its Location, in the Center of the Wood Insulator Plank.

Step 8: G. Connect the Thin Wire From the Power Supply (colored Blue/black/green) to the Black Wire of the Meter Using Your Wire (alligator Clips Are Useful).

Picture of G. Connect the Thin Wire From the Power Supply (colored Blue/black/green) to the Black Wire of the Meter Using Your Wire (alligator Clips Are Useful).

Step 9: More Cable Connections Located in the Center of the Insulating Board

Picture of More Cable Connections Located in the Center of the Insulating Board

Step 10: Confirm Electrical Connections. Take Reading.

Picture of Confirm Electrical Connections. Take Reading.

Check and confirm all connections and review these instructions.  After you confirm that all connections have been completed properly, then power on the laser machine. 

Using the touchpad, select Menu and set the laser power to 5% and the time to 3000 ms.  Power on the the laser from the touchpad and read the meter after the number settles.  To confirm that you have no problems, there will be no sparks or electrical arcing.  If sparks or electrical arcing then stop all work, power off the machine.

If the meter provides a reading and no sparks or arcing, then proceed by setting the laser power to 100%.

The current measurement at maximum output power should be 28 mA for a long life setting for a standard Chinese CO2 glass laser tube.  If the value is higher (such as more than 30 mA) then the internal gases will be consumed much more quickly during operation and the glass laser tube will need to be replaced more often.

Step 11: Adjusting the Potentiometer to Reduce Current

Picture of Adjusting the Potentiometer to Reduce Current

To adjust the current downward, consult your power supply manual.  DO NOT open the laser power supply enclosure and insert your fingers.  Using a grounding wire, ground everything when working on a power supply.  I was shocked six hours after power off, by touching the underside of the circuit card inside the laser power supply.  Always use a wire connected to ground to remove any lingering voltages stored in the capacitors inside the laser.  In many cases, the enclosure does not need to be opened and the potentiometer can be adjusted.


tr6canuck (author)2017-10-23

What company did you buy the 130w laser from? My Boss 150w laser was supposedly calibrated before they shipped it. It has always read 34 mA. If this was bad, why would they leave it like that?

AlexL293 made it! (author)2017-03-09


I'm also buy the old chinnese laser router, he moved but the laser not powered at all.. I bought the new power supply from Ebay ,but laser still not work.

Next I bought ten hi voltage resistors from mouser, 10mOhm every one, connect them in serial and one 100kOhm resistor close to ground wire to measure voltage.

When I push the "test" button i see the 1.16V at the 100kOhm resistor, it mean 1.16 kV for all resistors, and it not enough..

Maybe the power supply is defected or maybe the test mode not geneate the 100% voltage?

imbrokers (author)AlexL2932017-03-20


I have 3 of the above power supplies, None work
1 of them use to work, but then stop after a while, but then stops, so I added an additional fan to blow air onto the part below and the mosfet below it, it worked for a while then stopped working,

I have a feeling it is the part below that is a problem, as I see so many chinese websites selling them as replacements,

The problem I cant seem to find the correct name or more importantly how to test it?

Is there anyone who can also advise of which components are commonly faulty, because I have given up.


barbag (author)imbrokers2017-09-24

This white piece
is called the flyback, in my machine this part is responsible for all
the breakdowns, unfortunately to this day I did not find the origin what
this breakdown, if someone has some ideaes, I am taker .

ErichW5 (author)imbrokers2017-05-13

imbrokers I think you are talking about the flyback transformer. See: for a great description of this and some testing methods.

Veronica MorilloP made it! (author)2017-09-16

Si el tubo es de 100w reci. Cuanto es lo mA maximo

Csguillory (author)2017-02-22

We have a Chinese Redsail cm1290 laser engraver. The laser PSU reads L33 when we press the test button. Does anyone have any clues what it means? Our laser will not fire?

Esta disparando 33 mA. Acorta la vida del tubo.

CLIFFORDW8 (author)2017-06-27

I am not familiar with the 60W CO2 power supply. can some help me on how to troubleshoot my laser. there is not voltage going to the laser from the power supply HV outp (used high voltage probe 1000-1). this is a brand new power supply. Laser is from RedSail Corp frm China.

WillW63 made it! (author)2016-12-28

First if you not qualified do not touch high power systems,

Just changed the bridge and X2 safety Capacitor with a new Hexfet
Driver and flammable capacitor on one that blew the fuse
violently and it is back working.

Number of steps of concern is connecting the meter with alligator
clips externally on wood for those of no experience will follow.

The tube in mine the green wire goes directly to an
amp meter on the machine with the adjusting
potentiometer right next to it.

So no need to go through some extremley experimental
deadly test step by steps.

Some power supplies like the one with the 3 green plugs
has no internal adjustment.

Also a non insulated long screw driver adjusting anything
on any power supply, even more so on LIVE MAINS,
is not a really clever thing to do.

If the screwdriver tip hits a live conducting part like a components uninsulated
leg pin on the live side and that screwdriver shaft is touching
the power supply case then expect quite a big bang,
the 15 amp board fuse does not go quietly if
the power supply is shorted.

For those who do not trust the laser onboard coil meter then all
you have to do is disconnect it and put a trusted amp meter
in its place, two minute job a lot easier and safer
than dis mantling the whole machine.

I found it accurate when substituted so for me its fine and the
current potentiometer is right next door.

The adjustable resistor blocks on this circuit board should not
be played with if you do not know what they are for and
you really good with an osciloscope.

friklerouxloubser (author)2016-11-21

Hallo to ALL, I ask for help wrt the power supply for a laser cutting machine (see imageIMG_20161121_184616.jpg). A circuit diagram and the explanation thereof would be very helpful. Furthermore more detail identification of this power supply will be appreciated.

Kind Regards Frik

Skysurfer_uk (author)2016-11-11

Surely this only reads a current if the tube is firing? How can you tell if it's the tube, or the power supply?

Syamnathml (author)2015-10-27


I recently purchased a 40W co2 Laser Power Supply(ZR-40W), but it has only one output wire(red). I don't know where to find the negative connection.

LukeR22 (author)Syamnathml2015-12-09

Any success? I have a similar power supply - please help!

bharath3045 (author)LukeR222016-11-04

Need help i have similar power supply with only one red wire. How to do wiring.

Syamnathml made it! (author)LukeR222015-12-18

Check these

Syamnathml (author)LukeR222015-12-18

There are four terminals FG, AC, AC, L(-)

FG- Earth

AC- Phase


L(-) - Negative supply for laser

kamlesh2303 (author)Syamnathml2015-12-15

hi i've repaired many laser power supplies both output wires comes from HV transformer it seems from the picture that the other wire is one which is insulated by a tube wherever that one is connected you can solder other prob from there

mbowie4 (author)2016-06-20

How much does the multimeter pull down the current? I notice the laser intensity fades when I have the meter in series downstream from the laser tube. This makes me think that the meter must have some resistance and that the current reading may not be entirely accurate. At full power my meter reads 23.6 mA. Should I assume that is accurate?

MarkW219 (author)2016-04-15

Hi have just set up my new 60w chinese laser cutter and thr interface on it is in chinese and when i try the pulse button nothing happens and error message comes up in chinese. Ther does not seem to be any pwer going through the laser tube not sure what to do next any ideas.

faschessmaster (author)2015-12-15

Hi everyone

Three years ago I began using a laser tube machine.
The CO2 Laser tube worked perfectly well for three years.
But recently I started having problems, even with the new one.

So far I had no idea what might be the problem but, thanks to this article,
now I know that the power supply can be the principal cause of the CO2 Laser Tube Problems.

I also have a very important fact to share.
Our laser machine includes a power booster,
which doubles the current from 110V to 220V.
But guess what? The cables were inverted inside the power booster box,
and therefore, when we thought the machine received 220V, it really gets only 110V. But we solved the problem.

Thank you all for your comments.
They've really been helpful for me.
Success with your projects.

KurtS6 (author)2015-09-13

You mention being safe electrically when working with the laser power supply. Its also important to be safe with the laser optical output. An Infra Red Laser poses an extreme danger to the human eye. At my last job, we were required to wear protective goggles when in the room with an operating class IV IR Laser. Even when the tube was in its protective optical enclosure. Working on an open CO2 tube without goggles, without a plan for where the optical energy from the working aperture is going, and any leakage from the back mirror is going, and an IR scope to determine if there is any other optical issue, is an easy way to go blind.

churrosamperio (author)2015-09-09

wow thank you for your post, once i read that some reci tubes were modify the tag but i think was only a urban legend now i know its true! THANK YOU, REALLY!

Ragged Edge (author)2015-03-14

Really nice article. Thanks for the power supply information. First insight as to what might be wrong with my machine.

I purchased a new 150 Watt laser 3 months ago. (Chinese 37 X 48" bed, purchased through a U.S. Company. Tube says 160 watt) I have been very pleased with this machine (and the company I bought it from) as it did all that I had expected.I really like this machine for what I bought it for (Cutting shapes into 1/16" rotary cut maple veneer) and all the other projects I have been thinking up. Amazing machine!

From day one the machine has reflected some of the tube energy off the splitter mirror, onto the back case when running. This easily burns through masking tape placed on the case. Company said this was OK.
Two weeks ago it stopped cutting properly at the speed and power I normally run it at, speed 80 and a power of 100. After testing I would say it is almost half as strong as when I bought the unit.

What I have done to try to solve the problems:

- Leveled the bed of the table. It was slightly out and now has a consistent level over its entire surface.
- Changed the lens at the cutter nozzle and made sure they were clean.
-Removed, tested and changed the splitter lens at the ruby red laser, just in front of the laser. (did not help the burning on the case)
-Aligned all the mirrors correctly and cleaned.
-Tested the power supply with the equipment and instructions provided when purchased. (big resistor n such) Lots of power.

The unit has a mA meter built into it. When I first bought the unit when running at 100% power it would read around 40 mA now it will not go over 10mA when running at the same settings but the power supply test seemed OK.

This week the tech told me I should never run the laser at 100%. This was news to me as it is not in any literature I have gotten from them and when I first was setting up the machine tech support said nothing about this. We have a similar sized machine where I teach and they always run their machine at 100% without ant problems. Now I read your article!

My questions are;

Where did the mAmps go when the power supply test says it is OK?

Is it normal to have reflected energy from the beam splitter hitting the back of the unit?

Is it wrong to run it at 100% power? It does not run continuous during the day when in use.

Any insight on my next step from the form would be great as I am running out of Ideas.

Thanks for listening.

paul.kirkpatrick.9 (author)2015-01-09

How do you measure the laser output power?

Used the Mahoney CO2 laser power probe. There are videos on youtube showing how it operates.

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