Do you think this is a dead tube or power supply?

Hi everyone ,

For some time i’m trying to fix my laser but with no luck . No matter how much i move the wood up and down i cant get it to cut 3mm plywood . Today i noticed strange interuption in the tube while working . This is at 27% power making a simple circle for test ( 27% was enough before to cut 3mm plywood and sorry i dont have amp meter sadly :frowning: ) i tried increasing the power to 70-80 % but still it doesnt cut trough

Is it a dead tube or a powersupply issue or something else . I dont have any special controller the stock of K40 so i assume it should not change the power like this .

May I suggest reading the K40 Intro linked at the top of the site?

You’ll want to read in particular about analog ammeters and tube cooling, and describe here what you do for tube cooling.

Hi ,

So i may have destroyed it by teying out higher voltage . Will go tommorow and get everything needed to convert it to Analog . About the cooling i have and am always using distilled water with iced bottles that i change when the temperature goes up from 14-15 degrees and the stock water pump in a bucket . In general it was working coupple of months ago but i tried to add a beam combiner and afterwards i had to recalibrate it because the beam combiner didnt work out and it never managed to cut more than 1 mm . Its my mistake that i didnt look at the sound and tube and I’m not sure if the issue in the video is from after the failed attempt to upgrade or from before that . Worst case I’m thinking of making a bigger homemade co2 and I’m planing to order a tube with powersupply i can swap the psu and test it tho I’m not sure if the psu for 60w tube can be used for 40w tube but I’m assuming it should not be an issue if the only diference is the amperage and not the voltage between the new and old tube .

Once you have a current meter we can tell you more about the power supplies health based on the amount of current you are drawing.

A 60W supply can be used with a 40W tube as long as you keep the output in the range of your 40W tube’s current specs.

Sadly i cant find 0-30mA Ampmeter anywhere in my country (small eastern-european) best i found was 0-100mA … will have to order from Aliexpress and wait for a while .

Meanwhile while I’m waiting for the analog ampmeter can i use a digital mutimeter put at mA-ps for the test ? I know it wont be as pinpoint correct as the analog one but maybe.

It has a chance be more meaningful than the panel, since the digital one in the panel isn’t even trying to actually measure current. :smiling_face:

How close it is might depend on the multimeter and how it samples, though. It could be close, or it could bounce all over; it’s hard to say in general.

That should work but the digital meters’ response is such that you will not likely see quick changes.
I would give it a try.

1 Like

I’m sure we mean the same thing, but my digital meter jumps all over the place unless I use continuous pulse mode in the controller… The analog one doesn’t have this issue.

Didn’t think continuous pulse is possible with the K40 type wiring interface to the lps…unless you set power/pwm to 100%…?

First thing I’d suggest is to ensure that the tube is working properly. Look at tubes output at M1 to ensure the tube is in TEM00 mode or resonance.

I use targets I’ve cut out for alignment… and how I test the beam at M1

0 - 30mA meters are common from China, can’t order from them? I got a couple of mine from Amazon.

I’d use the 100mA if that’s all I could get, your visual resolution will be slightly less than 1/3 of the 30mA meter. They are probably physically the same size, so you could swap it out when you locate a 30mA meter.

You can use a regular dmm, but it might give you strange results depending on your pwm settings. It again, is a digital meter that samples.

Make sure it’s connected well, if not, that cathode could end up having a high potential on it.

There is a rather large bubble in the photograph that I would think should have flowed out of the tube… Were you running coolant when the video was shot? If so, doesn’t look like much is moving.

If you are dumping frozen bottles in the coolant, it probably isn’t distilled water anymore. Just the contaminant from the bottles are not a good idea.

I had a copper coil that I used as a heat exchanger to isolate the coolant, until my chiller was working… I also put the exchangers pluming into a beer cooler that I can keep mostly shut, keeping in as much cool as possible.

In actuality, you broke a working machine… and didn’t get it to work again…

IMHO, I wouldn’t recommend you do a diy if you can’t get this one to work like it originally did… this one is probably >95% functional, a new diy will have 0% functionality when initially built.

The problem with changing tube power sizes is that they have different physical dimensions. A 40W tube is about 50mm in diameter and 60W is about 55mm and the 80W tube is 80mm in diameter.

You will have to raise/lower the tube supports or the optics (m1, m2 and the head) to change this… not to mention physical length.

In simple terms

  1. properly working tube
  2. clean and aligned optics
  3. proper focus

They work…

In the end, I’d say it’s most likely to be number 2… that is the most common issue that causes this.

Good luck