Lincoln Electric SAE-300 HE Service Manual page 41

LINCOLN ELECTRIC SAE-300® HE Service Manual
tightening can destroy the rocker.
• Perform the Weld Circuit Ground and Short Circuit Test Procedure.
• If the weld circuit is not grounded or shorted and poor brush quality or contamination is
suspected, replace the brushes and seat them with a commutator stone or sandpaper.
• If brush quality or contamination is not suspected, clean the commutator by lightly stoning the
surface.
Stoning the commutator involves pressing an abrasive stone against a spinning commutator. This
procedure can be hazardous if done without proper training, tools and protective equipment.
Consult the commutator stone manufacturer's instructions before attempting this procedure.
Pitted and Arc Damaged Commutator:
If pitting and arc damage to the commutator is evident, the machine may have been used with
badly worn brushes. The brush spring tension may have been too low, or the brushes may have
been sticking in the holders. An out-of-adjustment rocker or a serious overload may also cause this
condition.
• Examine the inside of the brush covers and other parts that are close to the commutator. If there
is a significant amount of solder and debris that has been thrown from the commutator, the
armature will need to be replaced and the stator coils must be carefully examined and tested for
damage.
• Perform the Weld Circuit Ground and Short Circuit Test Procedure.
• If the brushes are worn out, replace them and resurface or clean the commutator as needed. If
the brush springs appear weak, discolored or damaged in any way, replace them as well. The brush
holder plates and retainers should be clean, smooth and undamaged so the brushes can move freely
as they wear.
• Check the rocker position. Be certain that it is aligned with or very close to the factory drill mark.
See Figure F.11. IMPORTANT: If the rocker position requires adjustment, do not over tighten the
rocker clamping screw. This screw should be tightened to a torque of 70 to 75 Inch-Lbs. Over
tightening can destroy the rocker.
Uneven Commutator appearance:
If the commutator appears to have some normal colored bars and some blackened bars, the
armature may be shorted.
• If excessive sparking is observed and/or the weld output is abnormal, the armature should be
replaced.
• If the commutator has uneven color, but there is no sign of serious generator performance
problems, the commutator may only need to be cleaned by lightly stoning the surface. See caution
note on commutator stone usage.
Examine the brushes:
The brushes and springs should all be in place and not be excessively worn. Brushes should be
replaced if they are worn to within 1/4" of the pigtail lead.
The pigtail lead of each brush should be positioned so it allows free movement of the brush while it
wears.
The brushes should be seated so that the face of each brush makes 95% minimum contact with the
commutator. Lightly stone the commutator to seat the brushes. See caution note on commutator
stone usage.
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