Nibbler: Won't Turn on

The armature is part of the motor, located inside the field of the motor, and is the only moving part. If the armature windings are shorted out, this can cause the nibbler not to power up. To check for a bad armature, remove the brushes from the nibbler before doing anything else. Some models may not have brush caps. The brushes cannot be removed until the housing is open. Remove the head from the main housing of the nibbler. Pull out the armature and inspect it for burn marks or melted insulation on the windings.

Replace the armature, if you notice one of these symptoms. There are three tests to use when checking an armature. The first is a continuity test. With the armature removed from the unit, stand it up on a bench. Attach one end of the ohmmeter to the shaft for ground and the other to the bar on the commutator. Move the probe to each bar on the commutator, checking all of the bars. If the ohmmeter shows a reading on one of the bars, this will indicate a short and a bad armature.

The second test you can do is a bar test to determine the resistance. Attach one probe to a bar on the commutator and the other probe on the bar right beside it. There will be a specific reading for this depending on the design of the armature, but most importantly is that there is not a large fluctuation here between the values, indicating a fault. If there is an increase in resistance, this will indicate there is a broken, or burned out, wire on the coil. If the resistance drops, then there is a short. Move around the commutator, checking each bar.

The third test is the 180-degree test. Attach the two ends of the ohmmeter on the commutator bars directly across from each other. There will be a specific set of readings for this, depending on the design of your unit. Once again, what is most important is that there is not a large fluctuation in values, indicating fault. If there is an increase in resistance, that would indicate a broken or burnt wire. If the resistance drops, that would mean there is a short. Continue this test on all the bars. If an armature fails any of these tests, it is recommended that you replace it. Install a new armature on the nibbler. Reattach the head to the main housing and reinsert the brushes and brush caps.

The carbon brushes supplies power to the armature by riding on the commutator. If the brushes are worn out, they cannot transmit power and the nibbler will not turn on. To check the carbon brushes, remove the brush caps on the side and pull out the brushes. Brushes measuring less than 1/8 of an inch are worn out and require replacement. Also, any damaged or broken brushes need to be replaced as they can also cause the nibbler to remain off. Always replace brushes in pairs. Install the new brushes.

The charger charges the battery, if your nibbler is cordless. If the charger is not charging, then purchase a new charger. To test a charger, set your multimeter to volts dc. For cord charges, attach the black lead to the outside of the charger and the red to the inside. The charger should be putting out a few more volts than what it is rated for because it will drop down when plugged into the battery. If your charger is putting out less than the recommend voltage, then replace it. For base chargers, the blinking light will give you all of the information you need, including if it needs to be replaced. Refer to your owner’s manual. Base chargers can also be checked with a multimeter set volts dc and attach the leads to the negative and positive side of the charger for readings to determine if the charger needs to be replaced or not.

The field is the second major component of the motor and creates an electromagnetic field, making the armature spin. If the field becomes overloaded or overheats, the field winding can burn out. Symptoms of a bad field are excessive sparks and a loss of power. Repair procedures will vary on all models as they are different, but the repair will be similar.

To replace the field, remove the carbon brushes first. Separate the head from the housing and pull out the armature. Remove the switch trigger and the cover around the switch. Detach the field wires at the switch. Remove any screws holding in the field and remove the field out of the housing. Examine the field for burn marks or melted insulation around the windings and replace, if you notice any of these symptoms or anything else out of the ordinary.

You can check the condition of the field by performing a couple tests. Using a multimeter, you can check the field for continuity. Set the multimeter to the ohmmeter and place a lead on each end of the coil in the field. You will have to perform this test for each coil in the field. If the reading is infinity for one, or more, of the coils, then the field is bad and requires replacement. If there is a major variance between the coils then the field needs to be replaced. Install a new field into the housing and secure it. Reattach the wires at the switch. Reinstall the armature and reassemble the housing back together. Reinstall the trigger and carbon brushes.

The power cord supplies the nibbler with power. Examine the cord for any breaks, cracks, frays or anything else out of the ordinary. Not only can a damaged cord not supply power, it is also a health and safety concern. To replace a damaged cord, remove the cover around the switch. On some models, you may have to disassemble the entire housing to access the switch. Detach the cord from the switch and remove the cord from the nibbler. You may have to transfer the cord guard from the old cord on to the new cord. Strip approximately ¼ of the insulation from the end of the new cord – crimp on new ends, if needed. Attach the cord to the switch and reassemble the housing.

The switch controls the flow of electricity to the motor. A broken switch will stop the motor from receiving power and will need to be replaced. The following repair procedure will vary on different makes and models but will be similar. To replace a malfunctioning switch, remove the trigger from the switch. Remove the cover on the housing around the switch. Remove the switch from the housing and take a photo of the wires to use as a reference for attaching the wires to the new switch.

With the switch removed, examine it for melting indicating overheating or sparking which will cause a bad switch. Replace the switch, if you notice anything out of the ordinary. You can test the switch with an ohmmeter. Attach a lead from the ohmmeter to each terminal on the switch. You should get a reading in the on position and not get one in the off position. This will indicate a good switch. If you are getting anything different, you have a bad switch. Attach the wires to the new switch and reassemble the switch back on the nibbler and close the housing.