How to know when to use Voc/Isc or Vtest/Itest for Thevenin?

[Zain]

should you only apply the test sources when there are only independent sources in the circuit. Also would it be valid to zero all independent source so that you are only left with independent sources and then apply the test source. It seems like i am always applying open and short circuit conditions when i should be applying a test source and vice versa :( Is the any systematic approach i can take to know when to apply what?

 

[scottdave]

Do you have a couple of sample circuits that you have done? If I recall correctly, if there are any dependent sources in the circuit, then you cannot "zero out" sources to find the Thévenin equivalent, and must use another method, such as a test source.