From technology aspect, owing to almost the same inner structure which is made up by a PN junction of the surface mounted diode and general diode, the testing methods of these two diodes are basically the same. R×100Ω and R×1 kΩ of multimeter are usually employed to test surface mounted diode.

　　1. Testing of general surface mounted diode

　　(1) Judgment of anode and cathode of surface mounted diode

　　There is usually a mark on the diode for the judgment of anode and cathode. When the diode is worn out and the mark becomes vague, check out by the Ohm mode of multimeter.

　　Adjust the multimeter to R×100Ωor R×1 kΩ mode and use the red and black probe to test the resistance of pins on the surface mounted diode. Then switch the probes and measure again. Consider the electrode that connect to the black probe as anode and the other cathode, then the first testing result is seen as forward resistance (several hundred ohm to several hundred kilohm), and another result is reverse resistance (dozes of kilohm to several hundred kilohm). Finally Choose the lower resistance figure out of the two testings as a standard.

　　(2) Judgment of performance of surface mounted diode

　　Testing of performance of surface mounted diode is often conducted under open circuit. The methods are as follows:

　　Adjust the multimeter to R×100Ωor R×1 kΩ mode to test the forward and reverse resistance of the diode. The one direction of current flow of diode indicates that the bigger difference between forward and reverse resistance, the better the diode will perform. If the difference is little, that means the diode is in bad conductivity; if both the forward and reverse resistance are large, that indicates the diode is in open circuit; and if both are small, that implies the diode is damaged. When the above three conditions appear, the diode need to be altered.

　　2. Testing of general special surface mounted diode

　　(1) Testing of zener surface mounted diode includes the following three aspects:

　　Judgment of anode and cathode on zener diode

　　① Alike general surface mounted diode, zener diode has its own pins which are not allowed to mistakenly connected. Anode and cathode can be recognized by the marks on the diode, for instance, the diode symbol, length of pins, color ring and color spots. If the marks are faded, Ohm mode on multimeter is also available.

　　② Testing of performance of zener diode

　　The method is the same as testing on general mounted diode. The forward resistance is usually l0 kΩ or so and the reverse resistance is infinite.

　　③ Testing of zener figure on zener diode

　　Adjust to l0 kΩ mode and connect the red probe to the anode and black probe to cathode. Until the needle no more swings, read the figure that the needle turns to under DC10 V mode. Then calculate the zener figure with the following formula: Uz=(10 - figure)×15 V

　　But pay attention: this method could be restricted by the voltage of battery of the multimeter under high resistance mode, which means it can only measure the zener figure of those zener diode that are below the battery voltage under high resistance mode.

　　(2) Testing of light emitting diode

　　Judgment of anode and cathode:

　　The two electrodes of LED can usually be simply recognized by eyes. Take the diode to a bright place and observe from side the shape of two leading wires. The smaller one is anode and the other cathode. When eyes can not tell the diode, Ohm mode on multimeter could be applied.

　　Adjust to l0 kΩ mode (starting voltage of LED is 2V and only when it is under l0 kΩ mode can it be conducted) and connect red and black probe to two leading wires. Test for at least two times and select the testing as standard when the needle deflects more than a half on the right side of multimeter and the whole diode is emitting subtle light. That means the black probe is connecting anode and the red probe cathode.

　　Okay, this is all about testing methods of surface mounted diode. If you want to know more information please click our website here: www.huixinelec.com

　　Note: the source text is from http://www.elecfans.com/