Plasma Cutter not arcing

[Nickrt]

I have a Thermal Dynamics Cutmaster 38 that I haven’t used in ~6 months. Went to use it tonight and it didn’t arc. The fan came on and air blew out of the torch but no arc. Frustrating when a piece of equipment doesn't work when you need it!

There are 4 lights on the machine. The AC light was on as was the compressed air light. They were both solid even when the torch was triggered. The DC light never came on.

Changed the consumables even though they were not worn. The torch and lead itself looks good – as does the PC board. No signs of burning on the board. Air pressure was set at 65 psi. Attempted to check continuity in the torch and it appeared to be ok. Have no idea how to check the board.

Struggling to understand why a machine that worked flawlessly since new with maybe a couple hours (still on original consumables with little to no wear) on it just stopped working.

Any suggestions would be greatly appreciated.

Thanks

[shorerider16]

First of all please don't take this the wrong way, sometimes it's the basics you miss that cause the problem. (And colourful language )
-Do you have a good ground?
-You say the torch continuity is good, but could the trigger continuity that activates the actual arc be the culprit. There are many wires that come out of the trigger lead and connect to various parts on the board. (At least on the plasma cutters I have seen without the cover)
-Is the output turned on. Sounds perpostrous, but it happened to us at shcool. Air pressure worked, all the lights showed good but no arc. Turns out the that the output dial was set purge. (Oops.)

[Nickrt]

I am hoping it is the basics that I am missing! Anything else could get expensive quick...

The ground is good. Was trying to cut a piece of clean sheet metal and had clamped directly to it. Good continuity on the grounding clamp to the ground stud in the case of the plasma cutter. Even with a bad ground the air should momentarily stop and the torch pilot should start within a second or two after I pull the trigger. When I pull the trigger the air starts but doesn't stop until 10 seconds (guess) after I release the trigger.

When I pull the trigger the air comes on. There is also a red led on the main pc board labeled torch switch that comes on when I pull the trigger. Checked continuity on the main red wire that connects to the torch to the board, the "pilot". Looks good as well. Now that I have the service manual I will check all the other wires to the PC board itself.

Checked and rechecked the setting hoping I was screwing them up. Dial set at 30 amps, switch set to run, power on.

Thanks for the suggestions. I am hoping that there may be something in the torch to PC board circuit that I can find and fix. Feels like a bad relay to me though. Something is not stopping the airflow and kicking in the pilot circuit.

[Wicked one]

I am hoping it is the basics that I am missing! Anything else could get expensive quick...

The ground is good. Was trying to cut a piece of clean sheet metal and had clamped directly to it. Good continuity on the grounding clamp to the ground stud in the case of the plasma cutter. Even with a bad ground the air should momentarily stop and the torch pilot should start within a second or two after I pull the trigger. When I pull the trigger the air starts but doesn't stop until 10 seconds (guess) after I release the trigger.

When I pull the trigger the air comes on. There is also a red led on the main pc board labeled torch switch that comes on when I pull the trigger. Checked continuity on the main red wire that connects to the torch to the board, the "pilot". Looks good as well. Now that I have the service manual I will check all the other wires to the PC board itself.

Checked and rechecked the setting hoping I was screwing them up. Dial set at 30 amps, switch set to run, power on.

Thanks for the suggestions. I am hoping that there may be something in the torch to PC board circuit that I can find and fix. Feels like a bad relay to me though. Something is not stopping the airflow and kicking in the pilot circuit.

This is going to sound really stupid but is your air dry and do you have a filter on it? We had a lot of problems with air quality and ours wouldn't fire because the air was to damp. Something to try . Jef

[mooseye]

I'm thinking that air light comes on when there is low air, not when it is good. Check your input pressure. Should be, what is it? 70 80psi.

[Nickrt]

Wicked One,

Funny you mention the air. The only thing I have changed since I used it last is my compressor. I have not checked to see if the air is dry, though I will. I do have a drier but not a real good one and I open the drain on the tank after every use. Would be awesome!

Mooseye,

The manual states to run at 65 psi, I have pushed it to 75 just to be sure.

The troubleshooting guide in the service manual confirms that the light is one when you have proper pressure. It also tells me that I have either a shorted torch or a faulty PC board (see below);

No pilot arc; Gas flows continuously; AC indicator
ON; TEMP indicator OFF; GAS indicator ON;
DC indicator OFF
1. Shorted Torch
a. Test torch and leads for continuity.
2. Faulty PC Board
a. Replace PC Board.


Thinking I still need to play with the multimeter. Saw a little leakage at the trigger switch though it was not shorted...

[KS2K]

I have a Thermal Dynamics Cutmaster 80xl that had the same problem you describe. The Thermal Dynamics tech had me check the air diffuser for a crack. Yup, it was cracked. I got a new diffuser and problem was fixed.

Unscrew the end off the gun, remove the cut tip. Next in line is a small ring with a step in it that sits down over the plasma generator. That is the diffuser. Evidently when its cracked, somehow it shorts out and you will not get arc. The crack was very small, hard to see, but it was there.

Now, the funny part. I live remote. Its a 180 mile ride to my LWS where I bought the Plasma. The little diffuser looks like a .50 cent part so instead of the ride, I call them and say send me 15. I wanted them in stock. Yikes, they are almost 20 bucks each. Needless to say, I returned 18 of them ha ha. Hope this is your problem, easy fix

Paul

[Steve]

Our Pac Master 38XL did almost the same thing . No pilot arc, No cutting anything. In the torch head are two spring loaded contacts that connect when the parts holder is put on. Its called Parts in Place signal. Meaning you got the torch head together correctly. Wont light off without it. Replaced the contacts and works fine now. Maybe yours is sorta the same.

[Nickrt]

Still working it...

Thanks for the advice guys. My torch has a start cartridge instead of a diffuser. It may be suspect though seems to work. Not exactly sure how to tell. The PIP switch checks out with the meter.

A call into tech support pointed me in a couple directions, including the starter. They also had me check resistance between the pilot wire and the ground; both while in purge mode and not. Supposed to go from closed to open (or vis-a-versa). No change, even when the trigger is pulled. Not sure what that means, hence another call to tech support is warranted.

In a previous call, they also indicated that I may have a bad PC board which they would sell to me for the same price they would sell a new machine, $1,000.... He indicated that he may be able to move on the price but that route does not sound promising.


For what it is worth the PWM (D99) light does not light up when I attempt to fire her up. It is supposed to.

[Nickrt]

Troubleshot it today with tech support on the phone. They are convinced it is the board... Offered me a $400 board but strongly suggests that I bring it to a service shop for installation. Figures ~2 hours labor.

So $550 for a new motherboard, unless I install it myself (which I am thinking of doing) or buying a new unit for $950... Hate to go back to the die grinder.