Hello,
I have K80 Chinese red laser with an 80W tube. At some point, it started making hissing, screaming sounds (adding the video). But screaming is not constant, like in video it only is when cutting, and sometimes it also stops while cutting.
I notice that the laser also started engraving a bit more poorly in order to engrave a bit better I have to move the focus point 2mm further away than usual.
Also, I am not 100% that it is tube screaming but I don’t know what else it can be.
Laser never reached high temperatures, and mainly operated cooled with ~10C - 50F distilled water.
Signs that the LPS is going bad.
but it’s weird…
LPS is grounded, I never used not distilled water. And it was in use only for ~7 months tops.
The first power supply on my K40 only lasted about 6 months. The same with my 60 watt laser. In fact, I went through two power supplies in 6 months on the 60 watt laser before the one I have now has lasted 4 years
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It’s likely the HVT in the LPS has a high voltage short.
The LPS is a consumable just like the tube. Under normal operation it will eventually die.
The LPS that I have heard are not quite that high of a frequency but that might depend on the job. It also sounds more like corona that and arc.
Pulse the supply with the test button on the supply and see if you can detect a crackle kind of his.
You can also take the cover off the LPS and in the dark see if you see corona in the supply. While your in the dark you can visually check around the tube to see if there are corona or arcs.
If you have an amp meter and the LPS is arching you should see it jump when it arcs…
These are lethal voltages to stay well away from the machine while observing.
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I’d check the output of the tube… It has the earmarks of it not being in TEM0 state, since it’s having an issue cutting…
It’s still probably a crop shoot on what’s causing it, lps or tube.
Many here have experience with a bad lps, so I’d follow their advise.
Have you actually looked at the tube to see if there is a visible difference when it ‘squeals’?
No missing cats… lol
Ones I’ve seen sometimes have some strange visual differences around the anode and cathode.
Never thought of the lps as a consumable … but everything has an engineered life span… I see more failed tubes on most of the sites I visit… lps failure here has always seemed excessive … maybe we’re to hard on things. lol
My original tube is on it’s way out… Have a new one on the floor here… Thought I’d abuse the old one, more than I have, before I swap it out…
Good luck
And then there is the currents you have been running the machine at. Many of those LPSs out of the gate will pump out 25mA but depending on your tube, you want to limit that to something the tube is designed and tested at for the MAX output. If your tube says it’s designed for 20mA at 80W and you’ve been dumping 25mA through it at max power then there’s gonna be some wearing of parts and the side effects can show up in your tube and your LPS.
I say this because I believe (and the teardown revealed) the HVT cannot take this level of operating voltage/current without eventually arcing across its winding or killing the internal diodes. Most failures I have dignosed are bad HVT’s.
You’re who triggered the comment… 
I know I’ve replaced many flyback transformers from old TV’s… So I don’t doubt that it could easily be responsible for this type of failure…
Of the ones (lps) you diagnosed, is there a common group of components that fail… Such as the driver circuits, windings of the transformer, current sense or ?
I’ve never been in one of these, haven’t had one to dissect … but have followed your HV trail best I could… thanks for that…
I also have an automatic internal cardiac defibrillator (AICD)… An external shock can cause it to think my heart is having issues, to whit it applies therapy … I.E. shocks the crap out of me… So I’m pretty careful.
LPS failure experience failures (1 is most frequent):
- HVT: winding short or interal HV diode stack open
- HV H-switch mosfets and or diodes
- HV Hswitch control IC.
- LV power supply
- Optocoupler
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