Miller Plasma Cutter Electronics Help

[UOfan]

Hi All,

I am trying to get an older Miller Spectrum 625 up and running. I took off the cover to blow out the dust and saw a blown something-or-other on a small circuit board attached to the power cable.

Does anyone know what the blown part is supposed to be? Maybe a small capacitor of some sorts?

The machine turns on - im still working through getting the torch good to go.

Thanks for any insight.

 

[American Locomotive]

Those were almost certainly MOVs (Metal Oxide Varistors). They're a special kind of resistor that's sensitive to voltage. If the voltage is below a certain threshold, they have an extremely high resistance and don't conduct electricity. If the voltage goes above a certain threshold, their resistance drops dramatically and they start conducting very well.

The idea is that if there is a brief spike in voltage, either on the incoming power or coming from the machine, the MOV will "clamp" the voltage down by turning into a dead short until the voltage drops below the threshold. They're basically a surge protection device.

MOVs naturally degrade with age, and each time they have to suppress a spike/surge, they damage themselves a little bit since that little disc has to absorb all of the energy. What happens is eventually the MOV goes permanently short and the incoming mains power quickly blows the MOV up. Once the MOV finishes blowing up, the device it's attached to usually keeps working normally as long as a fuse didn't blow.

It will probably continue to work fine as-is, but If you wanted to add new MOVs, you will want to find some rated for about 300v.

 

[UOfan]

Wow, thank you for the detailed answer. Posts like yours are the reason I read these forums. I really appreciate it.

For now, I’ll probably use as-is…and hope that my 50A breaker would trip before a power surge would destroy my machine.

Down the line I’ll look at replacing it. I’m trying to get a little smarter on electronics, this is a good excuse to learn.

 

[American Locomotive]

Keep in mind a breaker really won't do anything against a voltage spike.

 

[kctgb]

I’ll bet miller still has parts for that. Get ready to pay a lot. I had a miller welder from the late 50’s to early 60’s the local repair place was able to get OEM parts from miller to fix it.

 

[Beerhippie]

I’ll bet miller still has parts for that. Get ready to pay a lot. I had a miller welder from the late 50’s to early 60’s the local repair place was able to get OEM parts from miller to fix it.

I tried to repair a couple of our old Miller machines--a TIG w/snap-starter and a plasma cutter. Miller did still make the boards for them, but....

It was cheaper to buy new machines.

If those were MOVs--and I concur--they should be easy to replace. Just a little solder wicking/sucking and resolder.

 

[UOfan]

Thanks for all the input. In your guys opinion, is this a “do it ASAP” replacement or a “when you get around to it” thing?

 

[kctgb]

Thanks for all the input. In your guys opinion, is this a “do it ASAP” replacement or a “when you get around to it” thing?

Sadly, this is the reason why people buy Chinese welders and plasma cutters. Miller, and other big welder manufacturers, charge such high prices for circuit boards it forces people to buy Chinese. I had a dynasty burn up a circuit board three months after warranty ran out. It was $2000.00 for the circuit board plus labor to install it. No circuit board in a welder cost $2000.00 to make. I found the components online, they cost pennies compared to the price of the circuit board.
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[UOfan]

Sadly, this is the reason why people buy Chinese welders and plasma cutters. Miller, and other big welder manufacturers, charge such high prices for circuit boards it forces people to buy Chinese. I had a dynasty burn up a circuit board three months after warranty ran out. It was $2000.00 for the circuit board plus labor to install it. No circuit board in a welder cost $2000.00 to make. I found the components online, they cost pennies compared to the price of the circuit board.
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Thankfully I got this machine for $100, so I’m not in the hole already. I wouldn’t be willing to spend over 3-4 hundred dollars on a circuit board for a machine that already works (I just hooked it up to air, cleaned the torch components and got it to cut up to 3/16 mild steel at 35 amps).

At the end of the day it’s all fun and games for me, I don’t actually need this to make money or for my job. Hell, I could get away with just me angle grinder and abrasive saw that I’ve been using to cut metal for the last 6 years.

As others said, I’ll probably try to buy some components and solder them in. I’ll have to do quite a bit of practice because I don’t want to mess up the board….and I don’t do much with electronics (trying to get more proficient though).

I appreciate everyone’s input thus far!

 

[Beerhippie]

Sadly, this is the reason why people buy Chinese welders and plasma cutters. Miller, and other big welder manufacturers, charge such high prices for circuit boards it forces people to buy Chinese. I had a dynasty burn up a circuit board three months after warranty ran out. It was $2000.00 for the circuit board plus labor to install it. No circuit board in a welder cost $2000.00 to make. I found the components online, they cost pennies compared to the price of the circuit board.
0

In our case, we replaced the '80s transformer TIG w/discrete snap-start unit (that was always a maintenance problem with the points) with a new Miller Maxstar 150STH inverter for less than the cost of the parts for the old one. The plasma cutter we replaced with a Hypertherm--so all made in the USA, but still less than repairing the old Millers.

Thankfully I got this machine for $100, so I’m not in the hole already. I wouldn’t be willing to spend over 3-4 hundred dollars on a circuit board for a machine that already works (I just hooked it up to air, cleaned the torch components and got it to cut up to 3/16 mild steel at 35 amps).

At the end of the day it’s all fun and games for me, I don’t actually need this to make money or for my job. Hell, I could get away with just me angle grinder and abrasive saw that I’ve been using to cut metal for the last 6 years.

As others said, I’ll probably try to buy some components and solder them in. I’ll have to do quite a bit of practice because I don’t want to mess up the board….and I don’t do much with electronics (trying to get more proficient though).

I appreciate everyone’s input thus far!

The MOVs are there to protect the electronics in the unit from high voltage transients i the line voltage. If your electrical service is as fluky as ours, I'd make it a priority project.

The MOVs are not, themselves, particularly heat sensitive--no heat sinks or such required. Just get a good pencil-style soldering iron, some solder wick or a sucker for de-soldering, proper small gauge flux-core electronics solder and you're good to go.

 

[American Locomotive]

Thanks for all the input. In your guys opinion, is this a “do it ASAP” replacement or a “when you get around to it” thing?

I think it's a "see if the machine works first, then purchase the components" kind-of-thing.

 

[TheEquineFencer]

https://www.digikey.com/ is a good source for parts