F/R Switched While Running, Single Phase Motor

Get your voltmeter and unplug the lathe.

Remove covers from switch, motor access and anywhere else wires are present.

Keep lathe unplugged!

Place voltmeter in ohms first as we will just check wires and connections, this can be done safely without power.

Touch leads of meter together to confirm it now shows short.

If it has tone feature, turn on so sound on, faster this way.

First test is place leads across te main power wires on the plug, turn power switch on both forward and reverse.

It should show low resistance in these positions, if not, open wire, connection or fuse.

If you have a wiring diagram it helps, otherwise, you need to wing it.

You should be able to determine where the wires from the cord connect to the switch.

Leave one lead connected to the plug end, move the other to the switch.

Find the other end of the cord, check cord, next, closely look at how the switch works.

Go one step at a time, check ohms from the plug end to the test point.

This takes longer than just checking at the motor, but this forces you to inspect every detail.

Bear in mind that the ohmeter uses fery little current, so a dirty switch contact may read good.

Draw diagrams as you go because after you check with ohmeter and make repairs, then continue until you get every connection between plug and motor on both wires, you will plug it in and test it live, it is critical you know what wire is connected to where so you know what voltage to expect


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Best bet, when the motor was reversed, the start capacitor would have seen a higher than normal voltage as in addition to the line voltage, there would be a back emf from the start winding and the capacitor could have shorted out.

Can you start the motor by spinning by hand? Remove the belts to allow the motor spin freely. If it starts and runs normally, the the problem would be limited to the start winding circuit. A visual check of the centrifugal switch plus an ohmmeter check will validate its condition. Perhaps the easiest way to check the capacitor is with a substitution. The capacitance value doesn't have to be identical for this purpose. The start winding can be checked with an ohmmeter.
This is common on some machines, and most likely your problem
 
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