Miller Shopmaster 300 AC/DC

By SWN1158 (***)

Date 02-14-2017 21:03

We have a Miller Shopmaster 300 AC/DC. As soon as the wire touches the steel, it arcs, without pulling the trigger. I was told that this is happening because of a setting on the machine. Any idea which setting, and what it should be set on?

By Lawrence (*****)

Date 02-14-2017 22:44 Edited 02-14-2017 23:01

Hi Scott

When you say "wire" I'm assuming you are trying to do GMAW or FCAW... The Shopmaster is a multi-process unit that can do GTAW, SMAW, GMAW & SMAW... So it's CC/CV

First thing I would do is make sure the main control lever is set to CV

Also the "output contactor" toggle switch should be set on "remote"

Probably the next thing I would do is to switch out the Mig gun to make sure it's not a sticky trigger

If the machine is equipped with the optional gages you should be able to see if the unit is producing open circuit voltage... It should not when in the CV mode. the voltage should read zero in CV mode until you depress the trigger.

I would bet a Pastrami sandwich that the output contactor is in the "on" position.

By SWN1158 (***)

Date 02-15-2017 15:49

"Also the "output contactor" toggle switch should be set on "remote""

That was the problem Lawrence. Thank you so much!

By Lawrence (*****)

Date 02-15-2017 16:57

I apologize for the complexity of the picture Scott.

I my grandkids used up all of the crayons :)

By SWN1158 (***)

Date 02-16-2017 18:26

A red crayon would have really stood out.... maybe something like "Mommies Bright Red Stretch Mark" crayon.