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 TM 55-1925-204-12
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
4. MOTOR RUNS TOO SLOW UNDER LOAD.
Step 1. Check if line voltage is too low.
Check and remove any excess resistors in supply line, connections or control.
Step 2. Check if brushes are ahead of neutral.
Set brushes on neutral
Step 3. Check for overload.
Reduce load.
5. MOTOR RUNS TOO FAST UNDER LOAD.
Step 1. Check for weak field.
Check for resistance in shunt field circuits. Check for grounds.
Step 2. Check if line voltage is too high.
Adjust voltage to 115 volts (para. 2-17 g. (7) (d) 3.).
Step 3. Check if brushes are ahead of neutral.
Set brushes on neutral.
6. SPARKING AT BRUSHES.
Step 1. Check if commutator is in bad condition.
Clean commutator and reseat brushes.
Step 2. Check for broken or sluggish acting brush holder spring.
Replace spring. and adjust pressure.
Step 3. Check if brushes too short.
Replace brushes.
Step 4. Check if machine is overloaded.
Reduce load.
Step 5. Check for short circuit in armature.
Check commutator and remove any metallic particles between segments. Check for short between
adjacent commutator risers. Test for internal shorts in armature. Replace defective armature.
7. BRUSH CHATTER OR HISSING NOISE.
Step 1. Check for excessive clearance of brush holders.
Adjust holders.
Step 2. Check for incorrect angle of brushes.
Adjust to correct angle.
8. SELECTIVE COMMUTATOR (ONE BRUSH TAKES MORE LOAD THAN IT SHOULD).
Step 1. Check for insufficient brush spring pressure.
Adjust to correct pressure making sure brushes ride free in holders.
9. EXCESSIVE SPARKING.
Step 1. Check for poor brush fit on commutator.
Seat in brushes and polish commutator surface.
Step 2. Check if brushes binding in the brush holders.
Remove and clean holders.
Step 3. Check if brushes are off neutral.
Set brushes on neutral.
10. SPARKING AT LIGHT LOADS.
Step 1. Check for paint spray, chemical, oil or grease, or other foreign mateial on commutator.
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Clean commutator and provide protection against foreign matter.
11. COMMUTATOR OVERHEATS.
Step 1. Check if brushes are off neutral.
Adjust brushes.
Step 2. Check for excess spring pressure on brushes.
Decrease brush spring pressure but not to the point where sparking is introduced.
12. GROOVING OF COMMUTATOR.
Step 1. Check if brushes are properly spaced.
Space brushes.
13. BRUSHES WEAR RAPIDLY.
Step 1. Check for rough commutator.
Resurface commutator and undercut mica.
14. FIELD COILS OVERHEAT.
Step 1. Check for short circuit between turns or layers.
Replace defective coil
15. ARMATURE OVERHEATS.
Step 1. Check if motor is installed in location where ventilation is restricted.
Arrange for free circulation of air around motor.
Step 2. Check if armature winding is shorted.
Replace armature.
Step 3. Check for motor overload.
Reduce load to correspond to allowable load.
3-15
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