MAG255 Parts Substitution Card

This is the quick external-parts substitution card for the highest-value MAG255 crater-fill, spool-gun, and drive-roll splits.

Use This Card When

Complaint branch	Swap first	If the complaint follows the part...	If the complaint stays with the machine...
one-gun-only or aluminum-only failure	known-good spool gun and matching drive roll after chart-correct plain-steel base MIG is proven	keep diagnosis in spool-gun and drive-roll branch	move back to the machine only if base MIG also fails
erratic feed quality	correct drive-roll family and plain-steel wire baseline	keep diagnosis external and mechanical	move to feed-control branch only after the path is proven
wire creeps after stop	known-good plain-steel baseline while isolating or simplifying crater-fill behavior	keep diagnosis out of random board blame until crater-fill is isolated	move to crater-fill control logic if it still remains
sparks at wire tip with no trigger	known-good external path after proving safe setup	keep diagnosis out of spool-gun or gun blame if the symptom ignores branch swaps	move to discharge-path logic

Stop if the complaint follows only the spool-gun branch.
Stop if drive-roll correction restores feed quality.
Stop if crater-fill simplification changes the complaint before any deeper branch blame.
Stop using the card and open the full guide if stop behavior, discharge-path, and spool-gun evidence still overlap after external proving.