Ruida problem cn5 cn6 socket are not working properly

Hi guys, has anyone experienced something similar? I think the problem I’m facing is the LPWM1 not working properly
the power supply works normally, the tube does not firing. If I remove the cable (GND) from the socket (CN5) the tube firing but I can’t control the power and also the quality of the engraving is very bad as if it needs calibration.I tried to activate it as laser tube 2 from the machine settings by placing the plug opposite to (cn6) but I had the same result. I suspect it is something deeper in the board. specifically at LPWM1. Τhe power supply and the tube are new. the tube worked for a while with a power supply of 50w. then it stopped firing and the results were exactly the same there. I tried to upgrade it from 50w to 80w.
It works when I disconnect the cable (GND) from the socket (CN5) but it does not work properly.



If I understand the pictures correctly, the white wire and connector dangling near the power supply is the cathode return lead from the laser tube. It appears to emerge from the power supply near the high voltage anode lead, where I expect the cathode lead to be.

If that is the case, nothing will work correctly and you have exposed yourself to a potentially lethal high-voltage shock hazard.

Before proceeding: if the white lead is the cathode lead for the laser tube, it must be connected.

If the cathode was not connected it wouldn’t lase…

That wire is not in the first two photos…

If you remove the signal connector (circled in red) from the lps, it should fire with the lps test button (white arrow).

Do you have a voltmeter?

Should be sufficient to say there is over 30kV there and it takes time to bleed off…

It will reach out and touch you though…


It comes out of the back of the HV supply, drapes over the top, and obscures the AC input connector in every photo & video showing the supply.

If it’s not the cathode lead, it’s missing a great opportunity.

Unless the tube cathode is wired to the mate of that connector, in which case the cathode wire is arcing to the frame. That would explain all the other symptoms:

  • tube firing but I can’t control the power
  • quality of the engraving is very bad
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Very possible… but it’s not in this photo…

Have you run yours with no cathode connection?

I’m not going to disconnect mine to see where it arcs but I’d expect it to arc externally from the anode, not go through the tube. I think it would act just like a failed tube.

If there is no ground on the cathode, it isn’t going to excite anything and will never conduct.

Have you tried it…?

Either way, it needs to be connected… there is no disagreement there…

This isn’t how it’s supposed to be wired… if I’m seeing what I think I see…

Looks like L-On1 is wired to P, Ground to L and LPWM1 is wired to IN


I think it’s a wiring issue, including the cathode… just MHO…


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I finally changed the wiring
L-On1 - L

I had the same result.
I remove the signal connector from the lps the tube fired with the test button.
on the black cable (gnd) there is still a piece of cable which is left over.

A properly connected cathode wire operates within a few volts of ground potential, which is why the wire has ordinary low-voltage insulation instead of the bulky HV insulation on the anode.

I assume the blocky white connector on the white wire matches a similar connector on a wire from the tube’s cathode. That wire, which we have not yet seen, rests on the metal frame of the laser.

When the HV supply turns on, the high voltage puts the entire ungrounded tube at the same potential. Eventually, the low-voltage cathode wire insulation breaks down or one of the connector pins arcs to the machine frame, whereupon the tube lights up and the current flows directly to the frame.

When the tube fires normally, the voltage rises until the tube’s gas conducts to the (nearly grounded) cathode. The fact that the disconnected tube must conduct not only through that meter of gas, but another millimeter of cheap PVC insulation, is the key point: the tube voltage rises until something breaks down and the tube fires.

However, because the current does not return through the HV supply’s current-monitoring resistor, the supply cannot regulate it and produces as much current as it possibly can, unrestrained by the trimpot normally setting the upper current limit.


  • Is the tube cathode wire connected to the power supply’s cathode wire?
  • What does the white connector plug into?

the white wire is connected to the cathode of the tube

I see the white wire emerging near the bottom of the power supply going over the top of the power supply and ending in the rectangular white plug, which is apparently not connected.

My power supplies have a wire with similar thin black insulation emerging from that spot. That wire goes to the tube cathode.

The fat red wire with the bulky white tubular connector is the high-voltage anode lead for the laser tube.

The cathode wire is on the other end of the laser tube from the red anode wire. It will have relatively thin insulation.

Where does the wire attached to the tube’s cathode go?

the black cable is the tube and the white the power supply. in this case, the cable was probably white from the factory.
it is strange, the tube works and the power supply. when I disconnect (gnd) from (cn5) the tube firing.

I do not understand what you are describing, perhaps due to the language translations between us. I will use some of your pictures to illustrate what I am asking.

In this picture:


There are two visible wires:

  • The red wire going to the tube anode
  • The white wire (in your fingers) going over the top of the supply

In this picture:


What looks like the same white wire comes over the top of the supply and ends in a square white connector:

  • Why is that white wire disconnected?
  • What does it normally connect to?

In this picture of my laser tube and Mirror 1:

The tube’s cathode connection is the black wire at the upper left of the picture, attached to the tube through the glass seal. That wire connected to the power supply in my laser at the same physical location as the disconnected white wire in your laser.

Where does the corresponding wire in your laser connect to the HV power supply?

Please take a picture showing where the wire from the tube cathode enters the HV power supply.

finally i followed this diagram
L-AN1 → IN
L-ON1 → H
also i changed the output signal setting from low to high

I think now the laser works quite well, cut 3mm plywood 20mm/s 40% power.

I don’t think it acts like a resistor, the gas is an insulator.

There is no current flow until the potential across them (anode/cathode) becomes large enough for the ionizing to start. It would have to get across the gas gap with no other potential, or a very very high voltage, which would probably pierce the hv insulation on the anode, where it would arc.

I believe we don’t see lose cathode return lines arc, because the hv on the anode exceeds the voltage required to go through the tube, jump the open gap from the cathode to ground.

Maybe you have an HV meter you could measure this?

I haven’t done this, so I’ll have to bow to your analogy. But I’ve yet to ever hear the cathode arcing. My hv work was really with transmitters…


All of this would be moot if I could verify the tube cathode is connected to what seems to be the power supply’s cathode wire. Failing that, it would help to know what the tube cathode is connected to.

But I am unable to ask those questions in a comprehensible way and the eventual results seem to be acceptable, so … I’m out.

I think the way the photo is, you can’t see it’s connected to the black wire.

When it said it fire with the signal cable disconnected the lps/tube is working… It had to be wiring…

I wouldn’t call a disconnected cathode line discussion moot, how about more academic?

Your statements, many times, encourage an extended thought processing path…


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