Intermittent "squeal" from somewhere in the cutter

[scrappyjedi]

Unfortunately, after a short time running at low power (~20%) or PPI, it went back to the same behavior. The tube will intermittently squeal/screech, and the beam inside becomes the thin line that you see in the video instead of a more stable beam.

[Tech_Marco]

On meters setup, what frequency did you use?
By default, it is 20,000Hz. Try make it to 25,000 or 30,000 see if it make difference

Did you calibrat the Digital current meter. May be it is out of calibration. Worst scenerio, send back all components and let me set it up in my lab, except for the tube


Marco

[scrappyjedi]

It was still at the default- 20,000. I tried it at both 25,000 and 30,000 with the same results as before. (I did remember to hit the reset button after loading the settings, and I also read them back into LaserCAD to make sure they'd been uploaded.)

We haven't calibrated the current meter in a while, so I'll try that, but it is reading what I'd expect it to with the settings I've been using.

We actually ordered a new tube from you that FedEx says will arrive tomorrow. We might try it out and see what happens. We're building another cutter soon, so having a second one on hand wasn't going to be an issue, and I wanted one here just in case. A week of downtime is really backing up business here, and I can't afford much more.

[scrappyjedi]

Marco-

The new tube was delayed in shipping, but over the weekend, after completely rewiring grounding for the whole system (and not just the power supply and tube), we decided to swap the old tube back in and take our spare out. Everything immediately stabilized, so unfortunately I think that the spare tube itself was the issue. We'd originally replaced the old tube thinking it was dying, but that problem turned out to be a bad power supply that was fixed by installing the one we ordered from you last week.

The spare tube that was acting up had been in storage, but only for a couple of months, and only ran for a few hours in the cutter. It was ordered on September 15th- is it still under warranty?

[Tech_Marco]

Are youbsure the tube is bad? You should test the new tube again as I think it was yoir wiring issue that caused the trouble (bad contact or grounding are most common)

It is very uncommon the small SP tube is bad. Of course I won't say it 100% trouble free. If you sure that it is a bad tube, send it back to us for a replacement. Yes, it is covered by 6 months warranty from the date of purchas


Marco

[scrappyjedi]

We did test the new tube after redoing all of the wiring (including all the ground and the contact with the tube) with the same results. It also behaved in exactly the same way with three different high-voltage power supplies, including the new one that we just ordered and installed (that one is running fine with our old tube, by the way). Any time I applied low power levels to the tube, the beam would become unstable and behave as you see in the video. At high power levels it did cut well, but I need to run with lower power levels for several of the materials that I cut on a regular basis. As soon as we put the old tube back in, it worked perfectly with the same wiring that we were using with the new tube.

[swamidog]

have you considered using a lower power tube? there's a minimum threshold current necessary to achieve stable output. the value increases with tube size.

maybe you could use a lower power tube and run it more in an ideal power band.

We did test the new tube after redoing all of the wiring (including all the ground and the contact with the tube) with the same results. It also behaved in exactly the same way with three different high-voltage power supplies, including the new one that we just ordered and installed (that one is running fine with our old tube, by the way). Any time I applied low power levels to the tube, the beam would become unstable and behave as you see in the video. At high power levels it did cut well, but I need to run with lower power levels for several of the materials that I cut on a regular basis. As soon as we put the old tube back in, it worked perfectly with the same wiring that we were using with the new tube.

[Tech_Marco]

Hi Melissa

Can you send me the invoice number and I will create a RMA number for you to return the tube for replacement

I will set up a stage to test it and let you know what we find

Marco

[scrappyjedi]

Hi, Marco!

The order number was 202699, dated September 16. We actually ordered a replacement tube that arrived last week, so if we could work out a refund instead, that would be great.

And I'm very interested to know what your testing shows. I can provide the exact procedure we used to cause the failure here if it helps.

Thanks!
Melissa

[Tech_Marco]

Seems my staff didn't get my email and had not issued a RMA# for you
So, please wrap it up and send it back to us and attention "Marco"
I'll test it once received it


Marco

[scrappyjedi]

Marco,

I did receive an RMA email, and the tube is actually on its way back to you now, so that's all good! Let me know when you receive it and I can walk you through what was happening here on our end.

Thanks!
Melissa

[Tech_Marco]

Your tube received and we found no problem from preliminary test. It shine up a spot on concrete block. Now we're letting it ON for 10min see if anything change happened.

One thing I noticed that the tube is super dirty. There are smoke/ carbonate dust around the tube. It is very dirt. You may want to add suction fan in your work area or the tube or PSU won't last long because of the dust. Note that smoke may cause 'arc' firing near the HV connector

I'll post some pictures later

Marco

[scrappyjedi]

We cut and engrave a lot of cork and wood. There is suction/vacuum from the cutter, it just doesn't catch everything.

The laser would work fine above 7 mA or so. If I took it below that (or ran it at 600PPI, which is what I cut cork at), it might run okay for 30 seconds or so and then it would start the behavior shown in the video. After the squealing started, if I switched back to a higher power (in the 11-13 mA range), it would continue squealing for a minute or so and then eventually settle out. It did this with three different HV power supplies and two different AWC-608 controllers.

Ever since we put the old tube back in, we haven't seen the same behavior.

[Tech_Marco]

I have tested the tube for over 10min without seeing any problem. I could easily set it to 18mA and over on my tests in contrast to what you claimed 10~11mA when you did test in your machine (something was not right). It output very stable (I can take video to show). The problem should be the power supply you purchased. My staff told me that you purchased 60W instead of 40W. If you're doing high current cutting or engraving (over 4mA), then you shouldn't have any issue. But if you have to drive it in at low current (3mA or below) then you should use the same rating PSU. To offset this problem, you can use higher current setting and use higher speed to offset the high current.

I have tested the tube with two different PSU and I could see the difference. Both PSU were identical in circuit board but with different HV transformer. I could tune current as low as 1mA and vary it from 1mA to 2.5mA and notice that there was not much 'bouncing' light was happening inside the tube. The other PSU has to set current over 2.5mA. I talked to the supplier and was told that two transformers has different respond to the current output. One preform better with higher current but not at lower current. And it would laser longer. The other one has better response at lower current setting.

Normally, it is not often t drive a tube to low current because there is always a 'threshold' voltage/current need to be maintained to reach stable. For example, Reci 80W need 5~6mA to work while the 130W need 8~9mA. If you need to engrave or to cut something that is more delicate like paper or wax, then you better to turn higher speed to offset the issue.


I'll return the tube to you on Monday as I really couldn't find anything wrong with the tube


Marco

[scrappyjedi]

Marco, we had this issue with the tube using three different power supplies (I have mentioned this point several times in this thread), including two that were rated for 40W tubes. I ordered the 60W (which your web site actually lists at a 40W-60W, so I assumed it would be fine for a 40W tube) after having no luck with my first power supply or my spare. The video that I uploaded was actually shot while running with the original 40W rated PSU. We are currently running our old 40W tube with the 60W power supply with no issues, even at lower power settings. Based on that, I really do not believe this to be a power supply issue.

I realize that there is a low-current threshold, and I also know exactly where that is on my system and don't drive the tube below that. The conditions I was cutting under when it failed are the same ones that I've used for many, many months without issue before the new tube was installed, and they are exactly the same ones that I'm using now with my old tube back in the system.

Have you tested the tube at PPI yet, as that is another area I was seeing a failure? If I would run at 600ppi (power was at 49% on my 40W supply, which would have normally been about 13mA without PPI) for a few minutes it would lose power and start failing to cut, and then when I'd try to cut at full power again (no PPI), it would produce the same results as seen in the video. Again, this was with three different power supplies.