Repairing Harbor Freight 12" disc sander

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Old 03-09-19, 06:10 PM
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Repairing Harbor Freight 12" disc sander

I have an older Harbor Freight 12" disc sander. Model Number 43468. The motor just hums now and won't start. Replaced the switch.. No change. Pulled out and disconnected the start cap, discharged it and tested it with my analog VOM. Goes towards infinity, then returns to the left. Probably good. Still only a hum and no start

Does anyone here think the Run Cap is bad? Can I test the run cap like I did with the start cap? Any other fix ideas?

Thanks, Gang!

Canvasdraw
 
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Old 03-09-19, 06:21 PM
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That test shows the cap is not totally toasted but does not show if it's fully good. Need to do capacitance test. Same test on run and start.
Could be a stuck open centrifugal start switch.
 
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Old 03-09-19, 06:44 PM
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"Stuck open centrifugal start switch." Way above my knowledge. Care to unravel my lack of understanding? In simple terms?
TIA!
Canvasdraw
 
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Old 03-09-19, 07:20 PM
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Welcome to the forums.

In the link below is the manual for your grinder. Last page..... part #14 is the centrifugal switch.
You'll need to pull the end cap off the motor to see it. There is spinning weight on the motor shaft that presses against the switch.

Harbor Freight 43468 manual (pdf)
 
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Old 03-09-19, 08:39 PM
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Centrifugal start switch is closed when motor is starting so that the start cap is connected. Once the motor gets up to speed the switch opens to disconnect the cap. If switch is open on startup then cap is not giving the motor the boost that it needs to get going so the motor will just hum and not start. Can you spin the disk by hand and get the motor going?
 
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Old 03-09-19, 08:52 PM
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I can spin the disc and the sanding wheel will turn very slow with no torque. One time it did trip a breaker when I was spinning it.. Still hums.
 
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Old 03-09-19, 09:06 PM
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Thanks, Pete..

Is there a way for someone who knows little about electric motors to open the end of the motor
and check is the switch is open? Can it be cleaned in-place?

TIA!

Larry
 
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Old 03-10-19, 07:22 AM
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My best guess is a cap is bad. If you can, see if the centrifugal switch contacts are burnt. They may be losing contact so you can try cleaning/sanding them. Worst case is the motor has a bad/shorted winding. I have the same sander so I'll look at it to see how to get to the centrifugal switch.
 
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Old 03-10-19, 07:48 AM
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You need to remove the fan cover, pull the fan off and remove the end cover of the motor to get to the centrifugal switch. I'd do the capacitance test first to make sure the caps aren't bad. You will need a multimeter that has that test feature. Or just replace the caps and cross your fingers.
 
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