That glass-cased component is a diode; it could be a zener diode. The silk-screen component ID and/or symbol is not visible. A nearby empty location for D6 has the zener symbol.
Using the Diode Test range of a digital meter, a diode should show infinity ( "1." or "OL" ) one way, and from 400 to 700 the other way. If the diode is still in-circuit and being bridged by other components, the readings may differ.
This PCB does not have the 1-transistor, 1-SCR circuit that I wrote about; there are two small transistors and a flat-tab TO-220 component.
Have you checked whether adjusting the trimpot helps with the over-sensitive speed range?
Using the Diode Test range of a digital meter, a diode should show infinity ( "1." or "OL" ) one way, and from 400 to 700 the other way. If the diode is still in-circuit and being bridged by other components, the readings may differ.
This PCB does not have the 1-transistor, 1-SCR circuit that I wrote about; there are two small transistors and a flat-tab TO-220 component.
Have you checked whether adjusting the trimpot helps with the over-sensitive speed range?