Mystery component in motor speed controller

[jimmyblacksmith]

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?

 

[KlausST]

Hi.

I´m sure it was a diac.
If the motor still spins full RPM, then something else is defective (which makes sense, because the diac should not die alone)

Klaus

 

[jimmyblacksmith]

Hi.

I´m sure it was a diac.
If the motor still spins full RPM, then something else is defective (which makes sense, because the diac should not die alone)

Klaus

Thanks Klaus,
I replaced the triac just in case (although it tested fine), and I've also replaced C1, which leaked a little when I put 500v across it. Since replacing C1, I have an open circuit. No movement from the motor.

 

[FvM]

Tested without a diac? That's not expected to work.

 

[jimmyblacksmith]

Tested without a diac? That's not expected to work.

I mean to say: I replaced those other components, and replaced the diac. All components test OK. Open circuit.