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120 volt AC 1/2” Hammer Drill

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Hammer drill Intermittently Works

This like new powerful 1/2” Milwaukee 5380-21 corded hammer drill rarely will turn on.  When it does, it seems full power.  120volt ac is ALWAYS measured on both sides of both brushes when switch is depressed, but only rarely will it run. It’s completely dead, no click, no hum, no heat, no smoke! Brushes look smooth and almost new. Armature appears smooth, but I have not dismantled. I’m convinced the switch is OK. What’s my problem?

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Have you checked the switch is OK using a meter?

Here’s the service parts list for the drill.

It has a wiring diagram that shows the wiring coming into the switch and then where it goes to the brushes.

You said that there is 120V AC on both sides of the brushes, so for current to flow there needs to be a return path. You have the AC voltage at the brushes, check if the neutral return leg is OK. Looking at the wiring there is a black and white wire coming into the drill and connecting to the switch. Usually black is the neutral so presumably the white will be the active.

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The switch must be good when it delivers power to the brushes EVERY TIME the trigger is pulled. Even when the power is there, the drill is dead ——- usually. The Black lead is always the hot lead. White is neutral.


@Curt Larson

The switch may also pass the neutral through as well. (double pole switch?)

If white is the neutral then the neutral comes into the switch on terminal 7 and goes out from the switch to the brushes on terminal 4.

Reasonable assumption given the wire colour from term. 7 is white and goes to the brush and the other brush has black on it.


it sounds like the switch has something wrong internally that is causing intermittent use. Double check with a meter, especially since you say no matter what when it works it goes full tilt... the switch should not allow it to do that. It should control motor speed based on how hard the trigger is pressed.


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Curt Larson wird auf ewig dankbar sein.

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