Mystery component in a 240 volt motor speed controller.

Thread Starter

Jimmyblacksmith

Joined Jan 7, 2019
10
Hi,
This circuit is a 240 volt motor speed controller. There's a missing component (blank space above the triac), which looked like a zener diode, but it melted, so I can't identify it. I've tried diodes, thermistors, and diacs, but the motor only runs at top speed, or not at all. Can anyone tell me what the missing component should be?
 

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Alec_t

Joined Sep 17, 2013
14,312
Your schematic can't be right. You show the motor in parallel with the AC supply.
How did you test the capacitors?
 

Thread Starter

Jimmyblacksmith

Joined Jan 7, 2019
10
Your schematic can't be right. You show the motor in parallel with the AC supply.
How did you test the capacitors?
I posted a revised diagram above. The parallel motor was a typo. I tested the caps with an LCR meter, and then used an insulation tester to check for leakage at their rated voltage. I ended up replacing C1, which leaked slightly. I currently have a diac in the mystery position, and the circuit is open. Nothing reaching the motor.
 
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