Triac or Opto

[DanHouston]

Have a channel that was staying on, now it sometimes stays on.

I thought I had read somewhere that if you pull the opto and it stays on it is the triac. If it goes off it is the opto. I can't find where I read that and as I think more about this maybe that doesn't even make sense.

I know people just say switch with another chip and if it start working then it was the opto, and maybe that is the only test to determine which one it is?

Thanks,
Dan

[DaveM]

That is generally a good test. If you pull the optocoupler there is no input to the triac's gate. If the triac is still on either the triac is fried or you have corrosion/ dirt allowing leakage to trigger the gate.

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[tbone321]

Also check for water on the board near the opto's.  That can also cause enough leakage to trigger the triac.