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How do digital sewing machines fail? Is there often a visuall clue on the circuit board?

Discussion in 'Power Electronics' started by MidAtlantian, Feb 6, 2019.

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  1. MidAtlantian


    May 12, 2015
    Sir de Edd,

    When I remove the chip, and set the stage 2 output to low voltage from pin 4, the motor is at full speed, when I jump pin 8 to pin 1, it does not run. So I would assume that from the LM393 chip, things are OK. But before that there are resistors and caps, and the caps measure well within range!

    No! I had forgotten one, a large sort of oval shaped thing with a white casing near the main connector: a PME285MB. When I tried to measure the capacitance, it gave me the correct reading in one direction, and a very low one in the other. I looked it up, and was presented with photos it, sitting on one of “my” circuit boars. One comment said to unsolder it and resolder it. I did that and the speedcontrol board is now working! It was only with your help, and getting me to look at the circuit that I got this. Thank you!

    If there is anything you would be curious about in terms of what I did, or what components are where, please let me know. Funny that that particular capacitor has corrosion problems. There must be some interesting metals or electrlytes in it that causes that.
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