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Testing Miller welder capacitors
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Thad in AR. View Drop Down
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    Posted: 15 Dec 2021 at 5:23am
I have a Miller Magic Vintage.
1995 made to replace the MM200.
It will weld but not well. It has to be turned up higher than normal to weld and won’t produce a nice crisp ark.
Sometimes when welding lighter stuff the wire just turns red hot.
It used to have a nice crisp sizzle while welding. It does or now.
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really need the official make/model/info......
with that can find proper manual or 'howtofixit's

sounds like a 'wire feed' welder ?
If so, is it gas or flux core ?
gas ? , maybe wrong gas for the wire/metal ?
flux ?, OLD fluxwire, wet(humid) , wrong wire ??

if DC, maybe wrong polarity ??

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Thad in AR. View Drop Down
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Wire welder. Correct gas 70/20 per label and correct non flux 035 wire per the label.
Gonna buy a different spool of wire to try for the heck of it.
Gonna go over the bound wire and clamp and try to make sure all os good there.
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Taking apart terminal ends, wire brush and reinstall and TIGHTEN is a good idea after many years........ One problem i had recently is the little motor operated wheel that sets on top of the wire, and rolls the wire forward ... the little "teeth" had worn down and the wire was SLIPPING as it tried to feed...Wheel actually has two sets of teeth.. FLipped the wheel over and problem solved......... also i have heard of the sheath inside the feed cable getting dirty or damaged and causing the wire to DRAG or pick up dirt........ You could hold the gun out in the air and pull trigger and let several feet run out and see if it is CONSTANT and CLEAN...

this may help...
Like them all, but love the "B"s.
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Thad in AR. View Drop Down
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Originally posted by steve(ill) steve(ill) wrote:

Taking apart terminal ends, wire brush and reinstall and TIGHTEN is a good idea after many years........ One problem i had recently is the little motor operated wheel that sets on top of the wire, and rolls the wire forward ... the little "teeth" had worn down and the wire was SLIPPING as it tried to feed...Wheel actually has two sets of teeth.. FLipped the wheel over and problem solved......... also i have heard of the sheath inside the feed cable getting dirty or damaged and causing the wire to DRAG or pick up dirt........ You could hold the gun out in the air and pull trigger and let several feet run out and see if it is CONSTANT and CLEAN...

this may help...



Thanks Steve.
I just replaced the liner and now it feeds smoothly.
Sometimes when I try to weld the wire just turns red and won’t sizzle.
I’ve adjusted wire speed, temp polarity, and high lo switch.
From what I’m reading a lot points to the ground.
I know of others who replaced capacitors and was like getting a new welder.
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DaveKamp View Drop Down
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Thad, I'm not an expert on YOUR specific Miller welder...

But I know a bit about welders, especially Miller welders... and wire-feed welders.

I very, very, very highly doubt that the issue you're dealing with, is in any way related to the capacitors.

The MillerMatic Vintage is pretty straightforward.  Look at the diagram:


First off, the power control is totally switch-based.  The control board ONLY controls the wirefeed speed and operation.

The problem you identify, is a power SOURCE limitation... you're getting SOME power, but it is being current limited.

Current limitation happens simply because there's too much resistance at SOME point in the circuit, to allow current to flow at it's intended voltage.

In ANY welder, resistance at ANY point is an issue, but the lowest voltage, highest current points are those most seriously degrading to output... and that's where ANY welding system's greatest failure point resides.

Before you open it up, power it up, clamp a piece of scrap to the ground, set the welder on full-snot output, and lay down whatever bead it will allow, for about 30 seconds.  Then shut the machine off, and feel, an inch at a time, from one end of the ground wire to the other.  Feel the connections.  Now do the same with the gun.

Do you feel any warm spots?  If so, there's a high-resistance point in the circuit.  Fix that, and repeat the process, looking for another.

If you do NOT feel any warm spots, open it up, and find the current selector switch (S2).  It'll have big contact surfaces.  Clean them up with some Scotchbrite... not sandpaper, it will leave residue embedded into the contacts, which imposes resistance, and burns them up.

Every large cable connection must be suspected.  Unbolt them, scrub them totally clean, reassemble.

While you're at it, disconnect the AC power leads, clean up all those connections.  See any green?  it's corroded and bad.  Check the voltage selection jumpers, and wires on the back of the terminals- it's not unusual for copper in those to be cracked right  at the edge where the ring terminals are soldered on.

And keep in mind... you look at both ends, and they both look good...  that doesn't mean the middle is good.  A multistrand wire exhibits capillary action... surface tension will cause it to 'suck' moisture into the wire.  If you place one end of the wire into a bucket of water, it'll draw it into the cable the whole distance within an hour.  It can do it from moisture in the air.  You can frequently FEEL a 'hot spot' in the wire, and if you flex the wire, you'll feel a stiff, kinda crunchy spot.  Cut open the insulation with a knife, and you'll find it full of green fuzz.

Your gun/liner is part of the welding circuit, it HAS to be good inside.  If you feel hot spots in the gun whip, you'll probably find replacing the whole whip easier than pulling it apart to solve it.  You'll probably find that parts in it are melted from stray heat.
Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
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Had an old Lincoln engine driven welder, it began similarly where was failing to deliver a starting arc, are separate capacitors and a starting winding in those old machines that did fail over time, I replaced those capacitors and tested what I could of the welder generator windings where it came down to needing a rewind that no one did anymore for those older machines.  I threw in that towel some twenty two years ago where the fella that bought that old machine used it for parts to keep others running.  Spoke to him last week and was told there are companies now that are rewinding these as they were the best welders ever produced, they had nothing in comparison to replace them and he had that old frame rewound sold it to another guy who got a similar machine back online yet again.

Edited by DMiller - 22 Dec 2021 at 3:37am
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Thad in AR. View Drop Down
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Originally posted by DaveKamp DaveKamp wrote:

Thad, I'm not an expert on YOUR specific Miller welder...

But I know a bit about welders, especially Miller welders... and wire-feed welders.

I very, very, very highly doubt that the issue you're dealing with, is in any way related to the capacitors.

The MillerMatic Vintage is pretty straightforward.  Look at the diagram:

[IMG][/IMG]

First off, the power control is totally switch-based.  The control board ONLY controls the wirefeed speed and operation.

The problem you identify, is a power SOURCE limitation... you're getting SOME power, but it is being current limited.

Current limitation happens simply because there's too much resistance at SOME point in the circuit, to allow current to flow at it's intended voltage.

In ANY welder, resistance at ANY point is an issue, but the lowest voltage, highest current points are those most seriously degrading to output... and that's where ANY welding system's greatest failure point resides.

Before you open it up, power it up, clamp a piece of scrap to the ground, set the welder on full-snot output, and lay down whatever bead it will allow, for about 30 seconds.  Then shut the machine off, and feel, an inch at a time, from one end of the ground wire to the other.  Feel the connections.  Now do the same with the gun.

Do you feel any warm spots?  If so, there's a high-resistance point in the circuit.  Fix that, and repeat the process, looking for another.

If you do NOT feel any warm spots, open it up, and find the current selector switch (S2).  It'll have big contact surfaces.  Clean them up with some Scotchbrite... not sandpaper, it will leave residue embedded into the contacts, which imposes resistance, and burns them up.

Every large cable connection must be suspected.  Unbolt them, scrub them totally clean, reassemble.

While you're at it, disconnect the AC power leads, clean up all those connections.  See any green?  it's corroded and bad.  Check the voltage selection jumpers, and wires on the back of the terminals- it's not unusual for copper in those to be cracked right  at the edge where the ring terminals are soldered on.

And keep in mind... you look at both ends, and they both look good...  that doesn't mean the middle is good.  A multistrand wire exhibits capillary action... surface tension will cause it to 'suck' moisture into the wire.  If you place one end of the wire into a bucket of water, it'll draw it into the cable the whole distance within an hour.  It can do it from moisture in the air.  You can frequently FEEL a 'hot spot' in the wire, and if you flex the wire, you'll feel a stiff, kinda crunchy spot.  Cut open the insulation with a knife, and you'll find it full of green fuzz.

Your gun/liner is part of the welding circuit, it HAS to be good inside.  If you feel hot spots in the gun whip, you'll probably find replacing the whole whip easier than pulling it apart to solve it.  You'll probably find that parts in it are melted from stray heat.

Dave I suspect you are right on with this. Hoping to get a chance to mess with it soon. I’ll let you know.
It does have a new liner.
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