Few tips when you check the brushed dc-motor,
-disconnect all wires from motor
-turn motor slowly with hand and check is the rotor turning without jamming or stucking
....if so >> mechanical fail ... check bearings ...is field magnet loose...other loose parts.
Try to move the motor shaft axial and radial directions to find out is there right clearence in bearings.
-if motor has field winding(s) , look voltage and current values for field in name plate.
-calculate resistance and check by measuring
Usually brushed DC-motor has two, four or six brush holders.
-take away brushes so that only one pair is left in place in opposite sides ( difference 180 degrees )
-connect ohm-meter to armature wires and turn slowly rotor so that you can read ohm value for
every commutator plate pair. No higher resistance values are allowed.
Check every brush , no arc-marks , no grooves , equal lenght , not too short , copper conductor to brush is undamaged ,
if spring attached to brush , check that spring is undamaged and it makes enought pressure against commutator plates
Check brush-holders , brush must move freely in holder , check that brush size is suitable with holder.
If separate springs fo brushes are used , check pressure of the springs and test freely movement of springs
Check that all wires and contacts are in good condition
check the commutator plates surface condition
-no deep grooves
-no burned arc-marking
>> if arc-marks clearly occurs in one or two places , there could be armature coil failure
>> if arc-marks are random or all around , there is fail with brushes . ( low brush pressure , too short brush )
Test with low voltage adjustable power supply ( current limited or over current protected )
For motor with fixed magnet fied , connect supply and adjust voltage so that motor start slowly run. ( adjust current limit )
-check that motor run smoothly
-brake motor with hand , still should run smooth
-stop motor with hand and slowly let turn 360 degrees , no loss of torque allowed in any angle.
>> if point of torque-loss found , mark the position and check reason. ( fail in armature winding , commutator , brushes , brush-holders )
If motor has field winding connect mains isolated supply and adjust current 25...50% of name plate rating.
Do above tests
It is a great help in troubleshooting , if you know exact how the fault appeared and how the motor behaved in failed situation.
Good to remember, DC-motor commonly has tachometer included
and failed tacho can cause fault conditions ,
which could affect like fault on the motor.
So allways check the tachometer too.
There was some,
friends can tell additional tips...........