can I check Triac with ohm meter
>How can I check it (triac) inside circuit
Assuming you can disconnect the load from the circuit, and also assuming the
circuit is totally unpowered (triacs frequently are used to switch hazardous
line voltages), you might try the following:
1) With your DVM on low ohm range, measure gate(+) to MT1(-). On most triacs,
there should be an internal resistance of a couple dozen to a couple hundred
ohms. Certain logic level triacs, and sensitive gate triacs do not have this,
so be careful. Also, many circuits will have a gate ballasting resistor from G
to MT1, so you may not be able to get anything from this test.
2) With the DVM on low ohms, measure from MT2 (+) to MT! (-). This should
read high ohms (if not, the triac may be shorted out -- a very common failure
mode). Then, with the DVM leads still on MT2 (+) and MT1 (-), short MT2 to the
gate. When you do this, the triac should then read low ohms. Since it's a
triac, you should then be able to reverse the + and - leads, and perform the
test again. This is frequently the only "in-circuit" test you can make on a
triac in circuit with an ohmmeter.
These have worked for me in the past, but a lot of the time it's dependent on
the triac. Happy hunting, and again, be sure the circuit is unpowered before
measurement with an ohmmeter.