So my humble advice to the beginners is to think about every circuit or IC as a functional block – define the boundary yourself or from a schematic – make sense of the circuit does. To state the obvious, in a typical circuit block:
- will have a function name in the schematic - this contains important info regarding what the block supposed to do
- will generally has input, output, supply and control signals
Once you know that the input/output relationship does not hold (assuming that you understand what the block supposed to do), here are some of the steps that might helps
- Bias the circuit so that the block will have known state (or consider overwrite the input from a known source), use DMM to confirm all the DC pins, starting with supplies pins.
- Confirm the input output relationship – if it is not correct, break this block into smaller block and repeat the process (take a look at binary search debugging post: http://electroniccircuitdesignsharing.blogspot.com/2013/02/debugbinary-search.html).
- If the block is already an IC, check for part number, orientation, cold solder join, missing solder joints before “accusing” it as faulty part.
- remember that sometimes certain failure mode needs more than a DMM to be used (see http://electroniccircuitdesignsharing.blogspot.com/2012/06/why-oscilloscope-is-needed-for-circuit.html) , so if DMM cannot give you convergence, you should consider to use another instrument (depending on what this block supposed to do).