Dspark is on the right track here.
Some of my old Electronic Control projects were simple Solid State AC Lamp control circuitry [touch switches, Triac On/Off, Dimmers]. The Triac type Dimmers I made did have a Capacitor in series with the trim pot [the level control potentiometer].
On one, the tapped lead was run to the DIAC part of the gate circuit. Another simply used the pot as a rheostat [tapped lead tied to the output end of resistor].
Seems that both used a 0.22 MFD Capacitor and the pot was 500K.
It makes sense that you would get readings in the Mega Ohms area, that's the leakage across the Triac and the Capacitor. If there's an indicator lamp [like a LED], that would swing into conduction with a forward voltage above 2.0 VDC. Then you would also be reading the LED / Resistor / Incandescent Lamp series values.
Simply, the readings of >500K Ohms is normal, plus expected. If the readings were lower, that would be a sign of a failing component.
The measurements you got are from the Series-Parallel circuitry involved here. There's not a high enough voltage and current to "Fire" the Triac's gate into conduction, so the result is a very high Impedance [part pure Resistance, mostly Capacitive Reactance] to any varying power source. The DC power from the DVM simply fills the Triac up like a Capacitor, but since there's a difference in Potential on the gate and through the Anode of one part, there's a small leakage across the depletion region[s].
Also, the Capacitor / Pot trimming circuit is in Parallel with the Triac, so as tthe Capacitor is charged, it can discharge slowly through the other components [such as the Pot]. The leakage of the Capacitor would be in the Mega Ohms range too.
The only component with a relatively low resistance / impedance is the load [Incandescent lamp]. It's in series with the Triac and the trimpot circuit.
This is nearly impossible to describe with text! Best way to describe the thing would be with a schematic.
I'll draw up a few, then post later tomorrow. They are very basic, so shouldn't take a lot of time drawing.
Scott SET
