Oscillating Tool: Lacks Power

The armature is the power-producing part of the motor. If the armature has burn marks, melted windings or has suffered damage, it will reduce the flow of electricity and cause a loss of power. To inspect the armature, remove the brushes and open the housing of the oscillating tool.

For some models, the brushes cannot be removed until the housing is open. Remove any screws securing the motor in, and then lift up the motor and slide the armature out. Inspect the armature for signs of burn marks and melted windings. These are major signs of a problem occurring within the armature. Replace the armature if these signs of damage are present.

You can test the armature to check 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. Most importantly, you want to make sure 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 in the coil. If the resistance drops, then there is a short. Move the commutator around, 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, which would indicate a fault. If there is an increase in resistance, that would indicate a broken or burnt wire. If the resistance drops, then that means there is a short. Continue this test on all of the bars. If an armature fails any of these tests, it is recommended you replace it.

Install the armature into the field and position the motor assembly back in the housing. Reassemble the housing back together and reinstall the brushes with the brush caps.

A bearing is a device that is used to enable rotational, or linear, movement, while reducing friction and handling stress. A seized, or partial seized, bearing can cause the oscillating tool to have reduced power and may cause a burning smell, if the seized bearing is spinning against the plastic housing.

To inspect the bearings, remove the brush caps and pull out the brushes. On some models, you cannot remove the brushes until you open the oscillating tool. You may also be required to separate the head from the main housing. Lift up on the motor and pull the armature out of the field. Spin the bearings on the armature to determine which one is seized or partial seized. Bearings should spin freely with no noise.

To replace the lower bearing, remove the rubber ring. Not all models will have a rubber ring on the bearing, which absorbs vibrations. Use a bearing puller to remove the bearing. Clean the shaft and install a new bearing using a socket and tap into place with a hammer. The socket must only make contact with the bearings inner race to avoid damage to the bearing during installation. Reinstall the rubber ring.

To replace the upper bearing, use a bearing puller or a bearing separator, if clearance is an issue. Install a new bearing by placing a socket that only makes contact with the bearings inner race to avoid damage to the bearing. Tap in place with a hammer. Reinstall the armature in the field and place the motor assembly back in the housing. Reinstall the brushes, if you had to remove them once the tool was open, or reinstall once it is all back together, if there were brush caps. Reassemble the housing back together.

Replacement of shaft bearings will vary from model to model. Begin by opening the housing of the tool and lift the drive shaft out. You may have to lift up the motor to release the drive shaft. Remove any parts on the drive shaft to access the bearing. There may be retaining clips holding parts on. Use a bearing puller to remove the bearing. When doing so, use a socket that only makes contact with the bearings inner race to avoid any damage to the bearing. Tap in place with a hammer. Reinstall any parts that you had to take off to access the bearing and put the drive shaft back into the housing and then reassemble the housing.

Carbon brushes supplies the motor with electricity by riding on commutator. A worn out, or broken, carbon brush will cause the tool to have less power. To check the carbon brushes, remove the brush caps on the side and pull out the carbon brushes. Inspect the carbon brushes for signs of wear, chips or anything else out of the ordinary. Brushes measuring 1/8 of an inch, or less, are worn and require replacement. If brushes have uneven wear, replace them. Always replace brushes in pairs. Install the brushes into the tool and reattach the brush caps. On some makes and models, you will have to open the case of the tool to access and remove the brushes.

The field is the outside portion of the motor that creates the electromagnetic field. If the field has shorted out, it can cause a drop in power. To inspect the field and perform tests, remove the brush caps and pull out the brushes. For some models, the brushes cannot be removed until the housing is open. Open the housing and disconnect any wire terminals at the field. Remove any screws securing the field in place. Lift up the motor and separate the armature from the field. Clean the field with electrical contact cleaner and inspect it for burn marks and melted windings, indicating a short, overheating and sparking. If these signs are present, replace the field.

You can check the condition of the field by performing a couple of tests. Using a multimeter, you can check the field for continuity. Set the multimeter to an 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. Slide the armature into the field and position the field into the housing. Reinstall the screws securing the motor in place. Reattach the wires and reassemble the case back together. Install the brushes and brush caps.

The speed control switch controls the speed of the motor. If you increase or decrease the speed of your tool, but it remains at the same speed after changing it, then your speed control switch is malfunctioning. The following repair procedure will vary on all models, as they are different, but will be similar. To change out a defective speed control switch, open the housing of the tool. You may have to remove the screws securing the power cord clamp. Now, locate the speed control switch. Take a picture of the wire set up for easier reassemble. Disconnect the wires from the switch and then clean out the housing of all dust and debris. Attach the wires to the new switch and reassemble back into the case. Reattach the clamping screw for the power cord and reassemble the housing back together.

Some models have a circuit board that controls the oscillating tool when you turn it on and adjust the speed. Over time, and with use, this circuit board can overheat and start to melt, short out and have burn marks or a component may break loose from it. This can cause various problems for the tool, depending on the issue with the circuit board.

To check the circuit board, remove the brush caps and carbon brushes. Open the oscillating tool housing and locate the circuit board. Ensure all wires are attached to the circuit board before further diagnostics as a broken or loose wire may be the culprit. Remove the circuit board and examine it for burn marks, melting, broken components or anything else out of the ordinary that can cause it to malfunction. When replacing the circuit board, take a picture or draw a diagram of the wire connections to reassemble easier. Remove the old wires from the circuit board and attach onto the new circuit board. Reinstall into the housing and reassemble the housing back together. Reinstall the carbon brushes with the brush caps.