Component on circuit board from Ryobi Scroll Saw SC164VS.

Likely a DIAC Ed

Thanks Ed.

A sketch of the circuit is here.

In a week or two, can check Lee's Electronic Components here in Vancouver for a replacment; a C702 or a DB3.

Meanwhile I'm curious about the circuit. R5 adjusts the voltage delivered to the gate of the TRIAC. What do C2, R3, R4 and R6 add to that?

Thanks, ... P.

They control the timing (what phase angle) of the trigger to the triac. Maybe the simplest way to think of it is to picture 180 degrees of a sine wave and consider how long the triac conducts if the trigger is applied at 0 degrees, 1 degree, 2 degrees etc. When the trigger pulse "arrives" at the gate, the triac turns on and stays on as long as a certain minimum current, called the "holding current" flows. When the sine wave reaches 180 degrees there is no current so the triac turns off. The sooner in the cycle the triac is triggered the longer it conducts, providing input to the bridge and therefore power to the motor, thus controlling its speed. There's a lot more that could be said about triacs but that's a small overview. Ed

Ed, thanks for the explanation. Very helpful.

My immediate challenge is to find a replacement for the C702. From Web based documentation, DB3 is somewhat equivalent and may substitute.

Thx, ... P.

Good luck with the repair - my bet is that you'll succeed. :-) That was a nice schematic you drew. Ed