Hi all, having a power supply problem with my k40,

Hi all, having a power supply problem with my k40, currently on my 3rd psu in as many months, are they all junk or could there be an underlying problem? Thanks in advance

3 in 3 months seems a little excessive. I would start looking for the root cause in places other than the PSU. First thing to check for is arcing anywhere along the length of the high voltage circuit. This will fry a PSU quite quickly.

@donkjr any thoughts?

no arcing, they just start giving a little squeal at the start of a cut then randomly die after a few weeks.

Andy these psu’s don’t have current protection. So if one of the steppers is taking too much current then the 24v diode shorts and the whole thing tanks. So check if the carriage runs smoothly in x and y axis. If not correct it. The good news is that you can repair the power supply and you could wire a 1 A fuse in the 24v line to protect it. Where do you live? I’m in Sydney so happy to help if you are located near me otherwise you need to find someone closer to you.

It’s just the hv that seems to quit, the carage still runs but the laser stops firing. I still have one of the faulty supplies so if I can fix it I would love some more info. In Cheshire U.K. So a bit far to nip over to Sydney :slight_smile: thanks for the offer though.

Can you take one of the supplies cover off and take pictures of the components. Look for something charred.

I will take some photos in the daylight tomorrow. I didn’t see any charred or swollen components but I did just check the internal fuse and have a quick glance over the rest of it

@Andy_Parker you’re welcome☺

The squeel you mentioned is what my old k40 was doing when it was leaking power somewhere. I would check cables and insulation

Just added a short vid of the tube, i have also noticed that when it happens the monitor on my pc blacks out. They are both on the same ring main but not on the same socket. I have also taken a few pics of the inside of the last psu that i will post shortly.

Pics as promised

As you said nothing obviously failed from the picture.
Wish I lived closer…
Have you measured the 5 and 24v?
Does the red pwr led come on when you plug it in?
Did you replace the drive transistors I.e. those on the back side of the board.
Do you have an oscilloscope?

I haven’t measured the 5 and 24v as I assumed it was the flyback the power light does come on and it happily drives the stepper motors, just no output to the tube. I don’t have anything fancier than a multimeter unfortunately. I have not replaced anything on this psu, its straight out of the machine. Thanks again

@Andy_Parker the 5 and 24v are driven off one circuit and the high voltage circuit is dependent on the 24v circuit. The red led indicates that the driver ic works. Measure as @donkjr says the 24v first, if that doesn’t work then measure with an ohm meter whether the big fat diode close to the 24v 5v socket is a short in both directions. If so then replace it with a new one, i can send you one if needed. Btw i do have the exact same power supply​:grinning: Repaired it more then once :disappointed:

BTw you really should do this with it connected to your laser tube and stay away far from the output.
I say this to be ultra safe. But if you are only testing the DC and you have nothing but the AC connected to the input you should be ok.

It’s a stab in the dark. It’s possible that the 24v is not the right value, drives the steppers but not the HV section.
It’s strange the transistors are on the bottom and their solder connections looked a bit cold.

@donkjr ​ The 24v section is fed to a 7812 regulator which turns it into 12v. This is fed to the driver ua494 chip which drives the hv section. If the 24v breaks every goes dead.