Jig Saw: Won't Turn on

The armature is the power-producing unit of the motor, located inside the field of the motor. To check the armature for continuity, remove the base and take out the screws securing the case of the jigsaw together and separate. Locate and remove the carbon brushes. Remove any hold down clamps. Lift the motor assembly out of the case and slide the armature assembly free of the field.

On some models, the armature assembly will be attached to the gears and you will have to pull the armature free of it. Clean the armature with electrical contact cleaner. Inspect for any burn marks, or damage, that may indicate a problem.

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.

Attach the armature to the front gear assembly of the jigsaw and then slide the armature into the field. Place down inside the case and reinstall any clamps. Reinstall the brushes on the commutator. Reassemble the jigsaw case back together.

The carbon brushes ride on the commutator, supplying electricity to the armature via the commutator. If the brushes become worn out, they will not be able to make sufficient contact on the commutator, limiting, or not providing, power. To check the condition of the carbon brushes, remove the base of the jigsaw and open up the case by removing the screws securing it together. Locate the brushes and pull them clear of the commutator. Brushes 1/8 of an inch are worn and need to be replaced. Remove and replace the brushes from the holder and reinstall the case. Reassemble the case back together and reattach the base of the jigsaw.

The field coil is an electromagnet, used to generate the magnetic field needed in an electro-magnetic machine. If the jigsaw will not turn on, you can check the field for continuity. To do so, remove the base as well as the screws securing the case of the jigsaw together and separate. Remove the brushes. Remove any hold down clamps, then lift the motor up and slide the armature assembly free of the field. Disconnect the wires going in the field, making note of where they attach for when you reassemble. With the field removed, clean it with electrical contact cleaner. Inspect for any burn marks, indicating a bad field.

There is one test you can perform to check the field. Set the multimeter to the ohmmeter and place a lead on each end of the wire terminals on the field. If the reading is infinity, the field is bad and requires replacement. Install the armature assembly in the field (there will be a notch in the field indicating the front).

Place everything back in the case. Reattach the wires to the field and reinstall any hold down clamps. Reinstall the brushes and then close the case, securing it with the screws. Reattach the base of the jigsaw.

The cord supplies power to the jigsaw. Inspect the cord for any cracks, splits, cuts, burn marks or anything else out of the ordinary. Any of these indications, you will need to replace the cord as it cannot deliver electricity to the jigsaw and is also a safety concern.

If the power cord looks good, it may have come loose inside at the switch. Open the case by removing the base and take out the screws securing the case together. Check the connection issues at the switch, if that is the problem. If the cord requires replacement, remove it from the connection in the jigsaw. Remove the cord guard. Install the guard on the new cord and attach the cord to the appropriate connections inside the jigsaw. Make sure the guard is in place on the housing when you reassemble the case back together. Reattach the base

A broken, or worn out, switch, will not provide electricity to the motor when activated. To test and replace the switch, remove the base and then open up the case of the jigsaw by taking out the screws. On some models, you will only have to remove a cover on the handle to access the switch. Locate the switch and remove it from the housing. Remove the attached wires, making note of where they go for reinstallation. Inspect the switch for melting around the wire terminals as this will indicate shorting. If this is present, replace the switch.

To test a switch, attach a multimeter set to an ohmmeter and to each wire on the switch, checking it for continuity. The switch should read infinity, or zero, in the off position and when pressed, you should get a reading. If you do not get a reading in the on position, the switch is defective and requires replacement. Install a new switch, ensuring the wires are connected to the appropriate terminals. Install the switch in the housing. Tuck the wires into their channels and reassemble the case back together. Reattach the base.

Some jigsaw models may have caps on the side of them for easy access to remove the carbon brushes. Ensure these caps are tight. A loose, or broken, cap will not keep pressure on the commutator. Examine the caps for any signs of damage and replace. You can easily replace them with a flat-blade screwdriver to remove and reinstall the caps.

The brush holders hold the carbon brushes in place on the commutator and are located inside the jigsaw. A broken brush holder will not be able to support the brush, causing it not to make a connection on the commutator. To check the brush holders for damage, remove the base and open the case of the jigsaw by removing all of the screws. Locate the brush holders and remove. Examine them for breakage. To replace a brush holder, remove the brush from the holder and then remove the holder from the case – this will vary on models on how the holder is attached. Install the new brush holder and reinstall the brush. Install back in place, inside the case, and reassemble the case back together.