A newbie needs help

[Streamlined]

Hey yall, Im me to this forum and welding. I recently purchased a used mactools mm250 which from what I've read is a millermatic mm200. In the user manual it says that for using flux core with no gas you change the polarity so it grounds through the wire, opposite of usual set up. With that being said i can't get it to do anything. The wire feeds but won't spark. When the polarity is the other Way i can't get anything to stick. Just need some help. Lemmie know what info i can provid that i haven't. Thank you

[Bushytails]

I'm guessing you mean a MW250... Are you remembering to swap around both the power and ground connections? I think those have two bolts inside the cover, one with your ground clamp on it, and one to the wire feed assembly, and you need to unbolt and swap both of them around.

[Streamlined]

So i switched the ground clamp to the positive and the gun to negative. And i can't get it to spark up. I have a stripped bolt and I'm try to weld another bolt to it. Another question the wire that was in it kinda left a white dust around where i was trying to weld, there was no label on that spool do you know what kind that is? I was thinking aluminum but thats just a guess and not an educated one.

[Streamlined]

And yes Bushytails, correction the Mw250. Thank you

[Bushytails]

Hrmm, I've never seen one make sparks on one polarity and not the other!

Aluminum wire looks like aluminum, and weighs like aluminum... if you pull the spool out it will be very obvious.

Have you put in a new spool of wire?

Have you tried striking an arc directly to the ground clamp, to make sure it's not a ground connection problem?

[Streamlined]

I went and got a a new spool of flux core and installed. Its a silverish metal wire when i tried to weld with it, it left a silver/ white dust, i don't have the knowledge or experience to know what it is, that's why I'm asking. If it was obvious i assure you that i wouldn't be wasting anybodys time asking. I did strike the ground with the wire and it did nothing. So i should check my grounds, where should i check the ground on this machine?

[Bushytails]

What I'm confused about is why it worked on one polarity and not the other... simply swapping the wires shouldn't make a difference to whether it puts out power.

What is the serial number of your machine so I can pull up a manual?

[Meltedmetal]

Are you following the directions from figure 2-9 on page 9 of this manual?https://www.millerwelds.com/files/ow...54501v_mac.pdf

[Streamlined]

The serial is kf835317. Im confused also. Yes i followed those directions.

[Meltedmetal]

Page 5 in this manual. So you took the lead off at 3 and put it on the stud at 4 and off at 4 and put it on 3? Can you post a picture?https://www.millerwelds.com/files/ow...54501A_MIL.pdf

[Bushytails]

https://www.millerwelds.com/files/ow...54501A_MIL.pdf looks like that manual for that serial number.

Do you have a multimeter? Pop loose the wire feed pressure adjustment so you don't waste wire, squeeze the trigger, and measure the dc voltage across the two studs.

[Bushytails]

Since that model has mechanical voltage switches, work both the front panel one and the internal high/low one back and forth several times, as dirty contacts on them are a common issue on all welders.

[Streamlined]

Ill get amultimeter and check that Tom. Bushytails is there a way to clean those contacts?

[MAC702]

What I'm confused about is why it worked on one polarity and not the other... ...

DID IT work on the original settings before converting to FCAW?

OP, did you see the machine work before purchasing it? Is it possible we have an issue before swapping polarity to change processes?

Also, please edit your post to put the actual subject in the subject line. Every thread here is "needs help."

[Bushytails]

Also, please edit your post to put the actual subject in the subject line. Every thread here is "needs help."

I've been thinking we really need a sticky "How to post for help" thread, mentioning not necroing threads, posting using a helpful title, and to always include a machine serial number...