Archive for February 24th, 2011

This is Part 3.  You may want to read (part1) & (part2) first.

In this part I was going to probe the board to find where the signal was being lost for the controls. After mapping out all the connections and looking up the functionality of the ICs in the earlier postings I was confident I was going to track down the problem. I had the motor secured in my bench vise, the power supply and speed control board connected to the speed sensor feedback and mains 120v to a switch. When I turned on the 120v mains power I could smell something getting hot real fast. I had to work 30 second at a time and let the control board cool between tests. Something was not happy in the power supply! The heat was coming from a large 4watt 1.8K ohm resistor. I didn’t dare probe for more than 30 seconds because it was clearly getting too hot. But I pushed my luck too far (KA-BAM!).

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