Jig Saw: Excessive Sparks From the Motor

The armature is the power-producing unit of the motor, located inside the field and is the only part of the motor that rotates. To check the armature for shorts, which will cause sparking, remove the base and open the case of the jigsaw by taking out the screws. Remove the brushes and then lift up the armature and pull it out of the field.

Clean the armature with electrical contact cleaner only and wipe clean. Inspect the armature for burn marks indicating sparking. If you notice any burn marks, it may need to be replaced. You can double check the armature to verify its condition.

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 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 is a bar-to-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, there should not be a large fluctuation here between the values, which would indicate a fault. If there is an increase in resistance, this will indicate there is a broken, or burned out, wire in the coil. If the resistance drops, then there is a short. Move around the commutator, checking each bar.

The third, and final 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 important is that there is not a large fluctuation in values, which would indicate a fault. If there is an increase in resistance, that would indicate a broken, or burnt, wire. If the resistance drops, that would indicate 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.

Slide a new armature into the field. Once installed, ensure everything is secured back in the case. Reinstall the brushes and then reassemble the case back together. Reinstall the base.

The carbon brushes ride on the commutator in order to transmit power to the armature. When the brushes become worn, they will produce more sparks. To check the conditions of the brushes, remove the base from the jigsaw and then take out the screws securing the jigsaw case together and separate. Locate the brushes and pull them away from the commutator. Brushes measuring 1/8 of an inch, or less, are worn and require replacement. Remove the armature from the field. Clean the commutator with 600-grit aluminum oxide sand paper by rotating the armature in the direction of rotation, only to provide a smooth, even surface. Use a plastic scribe to clean in between the bars on the commutator. Reinstall the armature in the field and place the motor back down into the case. Remove the old brushes and install new ones. Reinstall them back in the case and reassemble the case back together. Reattach the base.

The field oil is an electromagnet, used to generate a magnetic field in an electro-magnetic machine. Over time, this part can build up a lot of heavy dirt, causing it to overheat, which can lead to problems such as sparking. To check the field for burn marks, indicating sparking, remove the base of the jigsaw. Remove the screws securing the case of the jigsaw together and separate the case. Remove the brushes, then lift up the motor and slide the armature out. Disconnect the wires attached to the field and make note of where they attach for reinstallation.

Clean the field with electrical contact cleaner only, and wipe clean. Inspect for burn marks, indicating a sparking field. If you notice any burn marks, replace the field as the burn marks indicate it's shorting out. You can perform one simple test to verify if the field is good or bad by using a multimeter to check the field for continuity, seeing if it has shortened. Set the multimeter to the ohmmeter and place a lead on each end of the field. If the reading is infinity, the field is bad and requires replacement. Attach the wires to the new field and slide the armature in the field and then place the motor in the case, ensuring it is secured. Install the brushes. Reassemble the case back together and attach the base.

The switch controls the flow of electricity to the motor. If the switch is defective, it can spark, melt and produce a burning smell. To replace the switch, open the case by removing the screws securing the case together. For some models, you will only have to remove a top cover on the handle to access the switch. Locate the switch and remove it. Make note of where the wires attach so you know where to reattach them. Inspect the switch for burn marks and melting, indicating a sparking switch. Attach the wires to the new switch and reassemble the case back together.