SMT parts how do I tell what they are?

Question

I have a circuit board I am trying to redesign but there are three SMT parts that have NO markings on them. They are extremely small and I used a magnifier to take them off and look for a PN or something. There are NO destinguishing marks on them. They all have two contacts so I figure they are either a resistor, a diode, or a capacitor. Does anyone have any idea on how I could test the to see what they are and what there values are.

Thanks

Answer 1

You can narrow it down to either a resistor or capacitor, and probably only a capacitor. The vast majority of SMD diodes will have some kind of marking. Most resistors (even commercial ones) will also have some kind of mark on them.

The majority of SMD components I have seen that do *not* have markings are capacitors, although I have seen a few resistors without marks, but rarely.

The best way to determine what kind they are is to temporarily remove them and use an RLC meter (with SMD mounts) to determine their type and value. Either that, or partially reverse engineer the board to find out how these components are used.

This meter is relatively new (there are several brands out, now) I haven't used them, but they look to fit your problem, well.
http://www.smarttweezers.com/?gclid=CLjxkY-No48CFQJsPAod00pHfA

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Answer 2

Use a multimeter on the resistance range. If it reads open circuit, it's a capacitor. If it reads a resistance value, reverse the leads. If it reads the same value it's a resistor. If it reads a different value it's a diode.