Laminate Trimmer: Won't Turn on

The armature is located inside the field of the motor and is the power-producing unit. If the armature is bad, it will not longer be able to produce power. Repair procedures will vary on all models, as they are different, yet the repair will be similar.

To check and replace an armature, remove the base, motor housing and then the tension springs on the carbon brushes. On some models, this is done by removing the brush caps on the side of the unit. Make a reference mark on the upper and lower motor housing. Then, separate the upper and lower half of the motor housing. Remove the collet from the shaft. Using a rag, or a thick glove, tightly hold on to one end of the armature shaft as you use an impact wrench to remove the chuck. Use a rubber mallet and tap the armature free of the housing. Clean the armature with electrical contact cleaner and inspect the armature for burn marks, indicating sparking and overheating.

To verify if an armature is good, or has gone bad, there are three tests to use when checking an armature. The first test 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 bad armature.

The second test is a bar-to-bar test, determining 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 is not 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 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 out wire. If the resistance drops, that would indicate that there is a short. Continue this test on all of the bars. If an armature fails any of these tests, it is recommended that you replace it.

Install the armature into the housing. You may need to tap it in with a rubber mallet. Reinstall the chuck with the impact wrench as you hold on to the opposite end. Reinstall the collet and rejoin the two halves of the motor housing, lining up the reference marks. Reinstall the tension on the brushes and reattach the motor cover and then the base.

Carbon brushes supply electricity to the armature by riding on the commutator. When the brushes become so badly worn, they will no longer be able to transfer electricity. Remove the motor cover and slide the tension springs to the side and pull the brushes out. Some brushes may have a spring attached to them and screwed in – remove the screw. Brushes 1/8 of an inch, or less, need to be replaced as they are worn out. Install new brushes and secure the screw. Reapply the tension spring and then reinstall the motor cover. Some units will have brush caps on the side of the unit for easy access to the brushes. Remove these caps by unscrewing them. Remove the brushes and install new ones. Reinsert the cap and tighten. Always replace brushes in pairs.

The field works with the armature to create an electromagnetic field, making the armature spin. If the field becomes overloaded, the field windings can burn out. Symptoms of a bad field include excessive sparks and a loss of power. Repair procedures will vary on all models, as they are different, yet the repair will be similar.

To check a field and replace it, remove the base and the motor cover off of the unit. Remove the speed control switch. Release the tension on the carbon brushes and then remove the upper bearing holder. Place a wrench on the lower shaft and use an allen key to remove the screw in the upper armature shaft. Loosen the shaft by turning the allen key only – the other wrench is used to prevent movement. Separate the two halves of the motor housing. Disconnect the field wires at the switch and speed control, making note of where they attach to beforehand. It is a good idea to take a picture for reference. Remove the brush holders from the motor housing and then the field wire from the brush holder. Cut the other two wires coming from the field as close to the crimped nut as possible, so you do not loose any wire length. Remove the screw securing the field to the housing and pull the field free. Clean the field with electrical contact cleaner and inspect the field for burn marks or anything else out of the ordinary.

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 is bad and requires replacement.

Install the new field, making sure the wires are lined up. Secure the field into the housing. Strip back ¼ inch of insulation on the wires that you cut, coming from the field before. Re-crimp the wires back together with a crimp nut. Reconnect each field wire back to the brush holders. Reinstall the brush holder back in the housing, with the insulators, and place the speed control back in the housing. Make sure every wire is tucked into its appropriate channel. Rejoin the two halves of the motor housing and reinstall the upper bearing holder and secure. Tighten the set screw in the armature shaft with a wrench and allen key. Reattach the brush springs, speed control switch, and the motor cover.

The power cord delivers electricity to the unit. Examine the power cord for any cuts, frays or anything else out of the ordinary. A damaged cord will not be able to supply electricity to the unit and can also be a fire hazard as it can spark. To replace a cord, remove the motor cover and disconnect the cord at the switch. For some units, you might have to remove the switch. Disconnect the cord and remove the cord guard. Attach the cord guard to the new cord and reconnect. On some cords, you may have to strip ¼ inch of insulation from the wire ends and crimp on new connectors, then reattach the switch. Reinstall the switch and then reinstall the motor cover.

The switch supplies power to the motor when turned on. Over time, the switch will wear out and will need to be replaced. To test a switch for continuity, you will need to access the switch and remove it. Remove the motor cover of the laminate trimmer. Remove the switch hold-down brackets and disconnect the wires at the switch terminals, making note of how they are connected for when you reassemble it. Attach an ohmmeter to the switch terminals. Turn the switch on and the ohmmeter should give you a reading, then turn the switch off and the ohmmeter should then read O.L or infinity. If the switch is not giving you these readings, then the switch is bad. Discard the old switch and install a new one. Attach the wires to the proper terminal and then attach the switch to the bracket and secure the bracket. Reinstall the motor cover.