# mini roubo #4: testing the switch on the planer

 Blog entry by kaaahl posted 03-14-2012 08:12 PM 7752 reads 0 times favorited 8 comments
 « Part 3: the death of a jointer -- help troubleshoot? Part 4 of mini roubo series Part 5: lots of yak shaving this past week. »

This will be my last post today, I swear. I just figured I would document this out in case other people run into power tool failures in the future.

First things first, I put the machine back together, except for the switch. I originally planned on using a voltage tester with live current, but I was nervous about that. The voltage tests that I had (read, that I stole from my dad’s tool box) looked old or cheap or both. But I found a video online to explain how to check circuits for resistance to see whether they are opened or closed.

The basic concept is you use an multi-meter and measure the resistance. If the two points aren’t connected, you get a “1” or an open message—there is a high level of resistance. If the two points you touch are connected, you get a “0” or closed message—there is virtually no resistance.

First, find multimeter.

Next, switch to measuring ohms and test multi-meter. When the two leads are touching, ohms (the green scale at the top) gets buried on the right—no resistance. When it’s open, it’s buried on the left—high resistance.

Unplug the machine from all equipment, we just want to test which circuits are connected, not the power in those circuits. I balled tinfoil around the plug end of the machine to complete the circuit on the plug side.

Examine switch. Black, white, and green come into the switch—black is usually hot, white neutral, green ground. Two yellows come out from the motor—one connects with white / neutral and the other connects to the other side of the power switch.

Now the testing.

Switch set to “off”, touch black and white wires with probes—> “0”—> so the plug isn’t shorted anywhere.
Switch set to “on”, touch black and white wires with probes—> “0”—> doesn’t really tell me any new information
Switch set to “off”, touch white neutral from power cord and yellow hot coming out of the switch—> “1”—> no power is making it through the switch, as it should be.
Switch set to “on”, touch white neutral from power cord and yellow hot coming out of the switch—> “0”—> switch did it’s job and power can flow through it.

I don’t know what it will tell me, but then I did the following two:

Switch set to “off”, touch yellow wire at switch and other yellow (normally connected to neutral)—“1”—> there isn’t a completed circuit.
Switch set to “on”, touch yellow wire at switch and other yellow (normally connected to neutral)—“1”—> there still isn’t a completed circuit.

I don’t know if their should be a completed circuit on the motor side when it is not running.

Anyway, it looks like I should investigate the brushes and see if I can find a screw extractor.

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