Resurrecting a dead plasma cutter...

[tomrscott]

I have an "opportunity" to pick up a Hypertherm 600 in very clean condition - except - it isn't working. /forums/images/graemlins/frown.gif

A service shop who looked at it said the torch works fine and it just needs the circuit board repaired/replaced. I've seen the circuit board and it is very clean but has a couple diodes that got fried, probably in the input or output. I can "finnagle" this unit for next to nothing $.

I have 25 years in electronics, so I'm not at all intimidated about tearing into a circuit board, but that is not to say there can't be something wrong that I can't fix, but the odds are probably fair that it is something simple that I can fix. If I cannot fix it, I could pay to have the board repaired by a third party shop who does these, or even buy a new board from Hypertherm and still be way ahead.

Here's the rub: Apparently plasma cutter manufacturer's don't provide any service information for the circuit board level, all they will do is swap out the board. I guess maybe they consider this a liability issue, however this is not a very complicated circuit board. There are third party shops who apparently will repair these boards for about half the cost of a new board, but I guess they're on their own too. Worst case, if a proprietary part like a microprocessor got fried, I might have to buy a new board from Hypertherm.

This is obviously a bit of a "pig in a poke", but I'm feeling lucky /forums/images/graemlins/wink.gif and even if I had to buy a new circuit board from Hypertherm it would still be a pretty good deal. If I can repair it, it's a "smokin' deal!"

1) (very long shot) Does anybody know anyone with connections to get circuit documentation for this unit? I can poke around without a schematic or parts list, but it's a lot easier with the proper documentation. I will check with the factory tomorrow, but from what I gather, they don't readily give this out. Maybe they used to? And maybe someone has something from an early or similar unit? Never know till you ask.

2) Does anyone have a Hypertherm 600 who would be willing to look at the components on their circuit board and read a part number from it if something is illegibly charred on this one?

With a bit of luck, I might be cutting out tractor weights in a week or two. /forums/images/graemlins/wink.gif

Call me nuts, but I have a good feeling about this. I'll let you know how it turns out.

 

[BGL990]

I'm an electronics geek as well (by training and by hobby) and I wouldn't even think twice. GRAB IT!! A couple smoked diodes is probably no big deal. If they are zeners it might be a bit of a challenge to figure out their voltage rating, but if they appear to be rectifier or signal diodes and you can guess at their proper orientation, just substitute something generic (1N4148 or 1N4000 series) and see what happens.

 

[WhiteRock]

Plasma cutters are great machines. I can understand the desire to get one at a good deal. They are quite expensive.

If I were paying very much for it, I would go in with the assumption that Hypertherm service/cost will be required. If you come out better, great.

This sounds like a recent Hypertherm model. Hyperthem appears to put a lot of engineering into their machines and I think you will find this board to be fairly sophisticated. Not that it can't be fixed, but it will be a high current regulated DC power supply. When the cutting process starts the power supply will attempt to maintain a high current flow. This means the voltage will be raised to maintain the start current. I don't know what the max voltage can go to, but BE CAREFUL. I suspect there can be some voltage there that can hurt.

The other problem I suspect you may face is the use of fairly expensive MOSFET devices for the high current regulated output. If you do not get all the bad parts replaced in the first attempt, you risk blowing another one of these expensive parts during test. On top of all this, they may use proprietary devices in their power supply to protect their competitive advantage.

I don't want to discourage you, but these might be some things you want to consider. I would do for the right price.

 

[PineRidge]

I'de grab it up in a heartbeat. After all even if you don't want it someone else would at eBay so it's a no lose situation if you can get it real cheap.

As far as printed circuit boards are concerned I know where you're coming from. We used to be a Bryant Dealer. Carrier and Bryant are one and the same. Whenever there was a problem with a circuit board and there were many, we could only get the complete board. The majority of the time it was a cold solder joint or a single fried component but the boards were treated as a throw-away replacement item.

Then again how many times do you ever remember seeing a computer technician carrying around a soldering iron for his repairs?

TC-40D SS web pictures click here

 

[bobodu]

</font><font color="blue" class="small">(
Then again how many times do you ever remember seeing a computer technician carrying around a soldering iron for his repairs?
)</font>

Too funny!! I think I have 5 computers that I built living here.I have one soldering iron...wonder where it is...... /forums/images/graemlins/confused.gif

 

[dummy]

What's the cost of a replacement cca? Some of the one's we use are much cheaper to buy than repair.

 

[slowzuki]

I have a Hypertherm 600, I would look inside if it didn't void my warantee... I would snatch it up, a new torch is over 600$ Canadian alone /forums/images/graemlins/shocked.gif

 

[aardvark]

I'm actually designing a throw away product right now. It's manufacturing cost is low enough, that paying our warranty dept to fix a return would cost more than just sending a new one. This product is going to be pretty neat. Two plastic housings, a couple connectors, two labels, and that's it. No screws, no seals, no test ports, nothing! Just going to sonic weld the housings together, and it's done!

 

[WhiteRock]

Sounds pretty neat. Do you mean a throw away plasma cutter?

Care to elaborate on the electrical stuff works? Would be interesting.

Thanks.

 

[TWINKLE_TOES]

Tom, if you don't see any fine pitch devices (25mil centers on leads) no IC's with Software version numbers tapped on the top or with little windows. If the circuit board is not more than two layers, If it's all discretes- R's C's Transistors (bipolar or FET) No larger geometry parts (2" x 2" epoxy blocks -IGBT's/SCRs) Part marking with established manufactuers(TI, National, Farchild, etc.) No custom magnetics then you can probably fix it. I would take a chance. If not the line starts at the street for guy's that are willing to try and I wanna be first in line.

 

[aardvark]

Oh no, sorry. Not a throw away plasma cutter. I got a little off topic I guess, I'm just fascinated by the whole "throw away electronics" phenomenon. I design marine electronics, I'm working on a small black box fishifinder right now (no display).

 

[WhiteRock]

<font color="blue"> small black box fishifinder right now (no display) </font>

Really neat! Does it mount on the rod and reel? /forums/images/graemlins/cool.gif Or does it just say fish below.... /forums/images/graemlins/grin.gif

 

[aardvark]

No, it interfaces with a dedicated display in other products such as chartplotters, etc. Although, it would be pretty neat to have a voice response unit. It could give directions, "fish below, wait, back up, now left, wait, forward, wait, now back up again, wait, go right, etc". I'm sure it would be a big seller. /forums/images/graemlins/smile.gif really though, it's similar in functionality to other black box fishfinders, just much less expensive.

 

[buy_sell]

I've done exactly the same thing. I found an old Linde 30 amp plasma cutter in the scrap yard. I opened it up and so far I could only find two things wrong with it. It had a burned 5 ohm 50 watt resistor and a broken pneumatic coupler for the gas. I repaired both of these problems but I haven't tested the unit, yet. I am going to make my own schematic before I go any further. If something else does blow up, I'll at least have a schematic and lots of photos. By looking at what initially went wrong, I'd have to guess that someone configured this unit to 208 and plugged it into a 230 outlet. The jumper block is set to 208 and I only use 230. I originally paid $30 canadian for the unit as scrap metal and invested $6 for the repair parts. Not too bad of an investment, if it works. A nice addition to my workshop.

 

[tomrscott]

Long posting, but some updates that might be interesting to some folks.

To answer some questions that have been posted, I have not pulled the board out yet and removed any parts to really test things, but with a quick visual inspection:

1) The board is very nicely done, but no fine pitch or unidentifiable parts that I've noticed so far. Looks like very high quality design from what I can see so far.

2) Everything is "through-hole" parts the ICs are all dips or large IGBT modules.

3) Scrutinizing it very closely with a bright light and magnifier, I could see four parts that look like they "might" have gotten too hot. Nothing is obviously scorched or charred. I like to order anything that looks suspect first and have it on hand when I begin working on the board. Usually a few dollars worth of parts not needed is worth the investment. I will often replace anything that looks even slightly suspect. If something is fried, other things could be degraded even if not completely failed.

4) Two of these parts were a pair of special MOS zeners. They looked kiind of grey and had a coating on them that could have been from overheating. 1N6303A, On Semiconductors, readily available.

5) One PWM controller UC3844A by ST, again a slightly greasy grey coating. Also readily available from stock.

6) A large Fuji discrete IGBT transistor. 1MB12-140 looks like it may have gotten hot enough to begin to vaporize the silicone heat sink grease it was mounted with. I've seen this before with power discretes. Makes a greasy grey smear all around the part and it's heatsink, which is what this looked like. This is a bit of an oddball part, no routine US distribution, the only available datasheet is half in Kanji characters with a bit of english sprinkled in for fun /forums/images/graemlins/grin.gif. VERY expensive to buy from FUJI, $33 each and $100 minimum, as in "THEY REALLY DON'T WANT TO BE BOTHERED! Any more expensive and I'd expect to get a cargo container full! One thing that makes this IGBT a little bit special is that it is rated for 1400 Vce, most IGBT families top out at 600 to 1200 volts. A 1200 volt part might actually be adequate, but I found a Fairchild part that is good for a bit more Ic, a bit more Vge voltage, and up to 1500 Vce, FGL40N150D. I am kind of figuring that in a plasma cutter, more is probably better. I'm sure transients can easily kill these circuits. Looking at it another way, this part is rated for the same values as the FUJI part at much higher temperature. These are routinely available in distribution for about $3, big difference! The parts are very similar and the Fairchild part should be a bit more robust, unless the Hypertherm circuit is designed very tightly to the FUJI part's performance. A little bit of gamble swapping it, but $100 is just kind of tough to stomache. Oh, actually I think the Fairchild part used to be a Samsung part, but Fairchild bought a bunch of discrete part families from Samsung a few years ago. I will wait to get the service manual and hopefully study the circuit very closely to see if there could be any very tight feedback or something that might be upset by a different part, but I suspect it is just a simple switch and will work fine.

7) I can't see any resistors or caps that look scorched at all.

8) My hunch? Like another posting, I am guessing that someone either hooked it up to the wrong line voltage, or did something to overload the output. They might have just run it way past its duty-cycle limits, but there is a thermal cutout mounted to the heatsink, so I think it would have protected itself from that.

Good news is that nobody has ham-fisted the circuit board and lifted pads or traces or otherwise butchered anything. It looks like new inside.

I may try to call their service department tomorrow and see if I can get someone who will talk about it with me, but I don't hold much hope for a circuit discussion with an engineer.

I did call Hypertherm today and managed to talk them into sending me a service manual. She even asked for the serial number of my unit, so I am hoping this means that the documentation will be an accurate depiction of my unit.

The schematic that I got from my friend at the service shop was kind of funny. Almost an "approximate" circuit diagram. I don't know if it is for an earlier model, or if they just intentionally obscure a lot of circuit details(?), but it clearly had about 1/4 as many parts in the diagram as my board, and what was there didn't match up very well with my circuit board. I am hoping that the documentation they are sending will be more accurate.

I've got all the parts listed above coming in a little over a week. I have pretty good connections with several industrial distributors having worked as an FAE in that industry for many years, so getting parts is not usually a problem. If you are any electronic designer getting to be friends with some FAEs at the big distributors can be worth its weight in gold. Digikey is nice, but they don't carry near everything.

I also went out this week and got some air fittings to upgrade my compressor with a good Cambell Hausfeld 5 micron air filter / vapor separator, and a desica gel air dryer cartridge. I decided to put a TEE on the output of my compressor with a separate quick disconnect and a 3' hose straight from the filter to the Plasma cutter, and the other long hose that bypasses the filter. That way I don't have to bother to use the air filter when I just want to fill tires and things, but I can use it for spray painting and other things that would like clean air. The 3' hose will help just a tiny bit to keep the flow rate up. My compressor is an 11cfm unit so it should be more than adquate.

I also have some work to do on the electrical outlets, converting to the 230V 50A socket that my welder and cutter are set up for. I have a circuit the previous owner ran specifically for a welder in my workshop, but the socket doesn't match. I'll also need to add a 20A 120V circuit there for my compressor. It doesn't like to run on a long extension cord.

Never been so excited to get cutting steel!!! /forums/images/graemlins/smirk.gif

 

[WhiteRock]

Great post! Neat stuff. Any chance of a pic of the board?

From what I have figured out about plasma cutter, I assume the big IGBT device is used in the switching power supply in a step up configuration. If this is the case, and you choose to substitute another part, I recommend paying close attention to the switching time specs if you can get them. If it is the switching device, the switching time is very important. If it is slow, the power dissipation in the device will be much higher and most likely not hold up even though the other specs are better.

The schematic should tell if it is in a switching power supply configuration. If this device is bad and configured as a switcher, the switching diode may be bad as well. Its switching time is critical as well.

I doubt if power input configuration damaged it. Probably duty cycle and/or shorting the probe (maybe trying to make bad comsumables work).

Just some thoughts....

 

[johnbilt]

Hi

I have a Hypertherm 1000 and a digital camera. Would you like a pic to see if there is a similarity ??

Sounds like an interesting project !! I assume you have a good voltmeter and a healthy respect for 240VAC.

I wonder what caused the failure initially. I have inspected the construction of the Hypertherm and would rate it as extremely high quality. Professional top notch ! If the power supply itself is the culprit, then you may be able to replace the obvious overheated parts and go from there. Inspect the coolng fans and verify this is not the source of the failure.

If the control circuitry is faulty, this will be difficult to diagnose without a logic diagram, and may induce the same failure again. Hypertherm service may be willing to offer advice based upon the defects you describe. They may have a history of these failures and know exactly where the weak points are.

Worst case, you would have to buy a new circuit board and still have a good deal on a plasma cutter.

John

 

[tomrscott]

Let's see if I can put a pic or two up...

Here's the Hypertherm and Miller, not a great shot...

 

[tomrscott]

Here's a shot of the circuit board from the AC Input end of the board.

 

[tomrscott]

Here's a shot showing the output end of the circuit board, and the air control plumbing.