Plasma Cutter Giant Tools LGK-60 not working

[CapLeaker]

I've got a Giant Tools LGK-60 Plasma Cutter here to repair.

Complaint: It does turn on, the display is on, consumables had been replaced, when the trigger is pressed the air valve opens and that is about all she does.

So I've opened that sucker up, checked the inverter o.k., checked the arc board o.k., came to look at the 400V 470uF main filter caps on the power supply and
You think there is sumtin wong here? All 6 of them look like that!

[CapLeaker]

Re: Plasma Cutter Giant Tools LGK-60 not working

Well guys and gals... The plasma cutter is FIXED! The last problem was that the control board didn't get the signal to turn on.

Besides the bad main filter capacitors, the trouble was actually on the arc board. The turn on signal was there for the air valve, but not for the controller board to turn on the inverter. I chased things around on the arc board and found 2 bad 22k resistors R6 and R15. R6 was way out and R15 was out of spec. Changed them out (look at the brown resistors) put it back together and I got 465V AC from the inverter, but no arc. Adjusted the spark gap FDQ to roughly 1.25 to 1.50mm and low and behold I've got the arc going in between them plates. Finally that case is closed and that stupid thing isn't smarter me.

This fix is for those that have the air valve go, but no AC voltage coming out of the inverter board when keyed. So there will be absolutely no spark from the wand, acts like dead.

On the arc board the trigger goes to CN5 (blue and green wire). The turn on signal for the controller board is on CN4 (the one on the right to CN5) and has a red, blue, green wire.
Between that blue and green wire should be 5V DC going to the controller board when triggered.

[Andrew F. Ali]

Re: Plasma Cutter Giant Tools LGK-60 not working

That appears as heat related damage. Pull them out and check values. I'd opt to change them out for a start.

[CapLeaker]

Re: Plasma Cutter Giant Tools LGK-60 not working

Oh yeah... those got hot alright somehow and needed to be replaced.

[sam_sam_sam]

Re: Plasma Cutter Giant Tools LGK-60 not working

Does unit have a IGBT module if it does after you recap it that would be the next thing to check to see if it is getting the command to turn ON

Make sure you replace the caps near the IGBT module if it has one

[CapLeaker]

Re: Plasma Cutter Giant Tools LGK-60 not working

The inverter has a bunch of MOSFET's 2SK4108 in it and those are good. The rectifiers diodes are good too. I didn't see any other caps on the inverter board, when I took it apart, but I am going to have another look. Have to wait on what the owner wants to do anyway...

[sam_sam_sam]

Re: Plasma Cutter Giant Tools LGK-60 not working

What micro controller does it have

[CapLeaker]

Re: Plasma Cutter Giant Tools LGK-60 not working

What micro controller does it have

I don't know... didn't take it that far apart (yet).

My theory right now, is that it is still a main filter capacitor problem. I did take a few of them caps out and checked them on my ESR meter. They show something like 20% down, with the ESR being at 0.22 Ohm. That doesn't mean they aren't breaking down at a higher testing voltage. I have a friend lined up with a proper tester that actually can charge the cap up to 400V and measures the leakage. We will see what happens.

[CapLeaker]

Re: Plasma Cutter Giant Tools LGK-60 not working

So I went and checked these caps with a proper high voltage tester. All of them have high ESR over 2.5 Ohms at rated voltage and leaking. That is exactly what I figured. I also came to find out that this Plasma Cutter was hooked up wrong at one point. That issue got fixed and the unit ran for a bit, then quit, then I've got it to repair.

[sam_sam_sam]

Re: Plasma Cutter Giant Tools LGK-60 not working

So That issue got fixed and the unit ran for a bit, then quit, then I've got it to repair.

Where I work at this happen all the time or at least it seem to be the case

[CapLeaker]

Re: Plasma Cutter Giant Tools LGK-60 not working

yeah, for some reason most of the time it always ran after an event for a lil while... I don’t think it was running any after that whatever happened to it..

[CapLeaker]

Re: Plasma Cutter Giant Tools LGK-60 not working

So...got the new replacement caps, put them in and the plasma cutter still does the exact same thing. No workie. Grr. Guess I am pulling the arc board next, unless someone has a better idea.

[sam_sam_sam]

Re: Plasma Cutter Giant Tools LGK-60 not working

Can you please post the photo of all of the boards in this unit
Thanks

[CapLeaker]

Re: Plasma Cutter Giant Tools LGK-60 not working

Well, I don't have all the boards out, but I did take out the PSU and the arc board. I've rechecked the PSU and that is 100%, even took the blue relay and the mosfet out and tested it o.k. Also checked the Thermistor (little black box) o.k.
Now to the arc board: All diodes, transistors, caps and resistors are good. Can't find anything wrong. Those green PTC's measure 450 Ohm and the other 530 Ohm. Kinda weird value or something?

[petehall347]

Re: Plasma Cutter Giant Tools LGK-60 not working

does it have an arc gap like some tig welders ?

[sam_sam_sam]

Re: Plasma Cutter Giant Tools LGK-60 not working

does it have an arc gap like some tig welders ?

I would also add this you need to find out if it is getting the command to ( fire )
start if not why not and do the 4 big caps getting any power

[CapLeaker]

Re: Plasma Cutter Giant Tools LGK-60 not working

does it have an arc gap like some tig welders ?

Yes (second pic, where the 3 blue HV caps are, marked F00), I cleaned those and played around with the gap to no avail.

I would also add this you need to find out if it is getting the command to ( fire )
start if not why not and do the 4 big caps getting any power

I know the trigger works, a relay clicks and air comes out. However, I am not sure if the arc board is getting the command to fire. I've got no schematics or anything to go by. The PSU is 100% and power is available.

[CapLeaker]

Re: Plasma Cutter Giant Tools LGK-60 not working

Here are more pics. All fets and diodes are good. All resistors at each of the fets are good. All big wire wound resistors are good... there is nothing I can see, but it still isn't working. The relay on the PSU is good, the relay on the arc board is good too. The temp sensors are good and slowly I am out of ideas. The control board is on the top, next to the inverter.

[petehall347]

Re: Plasma Cutter Giant Tools LGK-60 not working

continuity to torch for sanity

[petehall347]

Re: Plasma Cutter Giant Tools LGK-60 not working

no idea how they work but i see high voltage caps in there that may be leaking .. just a thought like .

[CapLeaker]

Re: Plasma Cutter Giant Tools LGK-60 not working

continuity to torch for sanity

been there and checked out good.

no idea how they work but i see high voltage caps in there that may be leaking .. just a thought like .

Well, I gave it more thought: The arc board (or HF board) only can arc, if it has power and that comes from the inverter board. If the inverter doesn't switch on, I am thinking that the arc board won't switch on either. That leaves the control board (or driver board for these fets) and the driver transformer board. After all, if the fets aren't driven from a PWM, then there is no power, right? Maybe the PWM is fubar? Food for thought.