Re: Bell and Howell TQII 1652 16mm projector
As a final test you could run it up on a resistive load (4K7) between pin 1 and 3. You would have to disconnect the Zener from pin 3 and connect it to pin 4 to get the motor running.
You seem to have a large tacho signal so it is difficult to believe this could be a problem although you do say the scope image is when the tacho is disconnected so it would be good to see it when it is connected.
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