Table 7-4.--DC Generator Troubleshooting Chart
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.
Clean or dress commutator.
Brushes not making proper contact
Free, if binding in holders. Replace and reseat if
Newly seated brushes not contacting sufficient
Run in by reducing load and using a brush-seating
area on the commutator
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
Open filter choke
Broken brush shunts or pigtails
Output Voltage Too Low
Prime mover speed too low
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
Faulty voltage regulator
Adjust or replace.
Check meter readings against nameplate ratings.
Excessive brush pressure
Adjust pressure or replace tension springs.
Align units properly.
End bells improperly positioned
Straighten or replace.