Table 7-4.--DC Generator Troubleshooting Chart
Probable Cause
Remedy
Failure to Build Up Voltage
Open field resistor
Repair or replace resistor.
Open field circuit
Check coils for open and loose connections.
Replace the defective coil or coils.
Tighten or solder loose connections.
Absence of residual magnetism in a self-excited
Flash the field.
Dirty commutator
Clean or dress commutator.
High mica
Undercut mica.
Brushes not making proper contact
Free, if binding in holders. Replace and reseat if
worn.
Newly seated brushes not contacting sufficient
Run in by reducing load and using a brush-seating
area on the commutator
stone.
Armature shorted internally, or to ground
Remove, test, and repair or replace.
Grounded or shorted field coil
Test, and repair or replace.
Shorted filtering capacitor
Replace.
Open filter choke
Replace.
Broken brush shunts or pigtails
Replace brushes.
Output Voltage Too Low
Prime mover speed too low
Check speed with tachometer. Adjust governor on
prime mover.
Brushes not seated properly
Run in with partial load, use brush-seating stone.
Commutator is dirty or film is too heavy
Clean, or if film is too heavy, replace brushes
with a complete set of proper grade.
Field resistor not properly adjusted
Adjust field strength. Tighten all connections.
Make shim adjustment.
Reversed field coil or armature connection
Check and connect properly.
Output Voltage Too High
Prime mover speed too high
Check speed with tachometer. Adjust governor on
prime mover.
Faulty voltage regulator
Adjust or replace.
Armature Overheats
Overloaded
Check meter readings against nameplate ratings.
Reduce load.
Excessive brush pressure
Adjust pressure or replace tension springs.
Couplings not aligned
Align units properly.
End bells improperly positioned
Assemble correctly.
Bent shaft
Straighten or replace.
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