Archive for November, 2010
I’m attempting to diagnose a problem with the motor power supply for a small metal lathe. This is part 2 so you may want to read part 1 first.
I know the 120v AC mains are flowing through a monolith bridge rectifier and coming out as a fully rectified pulsing DC signal. This rectified DC signal is smoothed out by a very large 220v 300uF cap which is then supplying “somewhat clean” DC to the (+) terminal on the motor. Notice I didn’t say anything about a transformer because there isn’t one. That means the voltage to the motor is not being stepped down; just full wave rectified and smoothed out with a large cap.
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In this blog posting I’m attempting to diagnose a problem with a motor power supply for a small metal lathe. I will document how I evaluate a circuit board and repair it if possible.
I’m confident the problem is with the power supply because when I plugged in the lathe nothing happened. The motor doesn’t flinch even when the speed control is turned to high. Plus there is no voltage at all across the motor terminals so that does make sense. Something in the motors power supply is preventing power getting to the motor terminals.
There are always a few steps I take when attempting to repair something electrical.