Testing Zener Diode
Fast And Simple Way To Accurately Test A Zener Diode
Analog multimeter is the right meter to test a zener diode. First, search from your favorite data book what is the zener diode code represent. I highly recommend Philip ECG semiconductor master replacement guide. When you have determined the zener diode voltage, it is easy to check with your meter to see if it leak, open or shorted. For your information, a zener diode with 2.4 volt to 12 volt should have two readings when measure with an analogue meter set to times 10K ohm range. But these readings is not shorted reading!
Let me explain, when you place your probes across the zener diode of 2.4 volt using the times 10 k ohm range, one way will show a full scale reading (red probe to cathode and black probe to anode) which mean the needle will moved towards the 0 ohms scale while the other way (black probe to cathode and red probe to anode) the needle will point to around 2- 5 ohms! If both ways of testing and the needle point to the 0 ohm scale then the zener diode consider shorted. When you measure a 6.8 volt zener diode, as usual one way will point to zero ohms while the other way will show a higher resistance which is in the 20 to 50 ohms. These are the characteristic of a good working zener diode.
When you measure a zener diode from 13 volt and above, it should have only one reading using the times 10 K ohms range. That's mean the red probe to the cathode and black probe to the anode. Reversing the probe should not show any reading. If the result shows two readings then the zener diode is shorted or have leakage. Start taking out zener diode from your component's rack and do some testing, compare a good zener diode and a shorted one. It would'nt take you a long time to become a pro in accurately testing a zener diode. One more thing, only replace a zener diode with the same or higher wattage. If possible use the exact voltage.