Testing Zener Diode

Analogue multitester is the most suitable meter to accurately test a zener diode. First, find from your semiconductor data book  what is the zener diode code represent. I strongly recommend Philip ECG semiconductor master replacement book. When you have found the zener diode voltage, it is simple to measure with your analog meter to see if it leak, open or has developed a short circuit. For your info, a zener diode with 2.4 v to 12 v should have two readings when check with your analog multimeter set to the range of times 10K ohm . But these readings is not a direct shorted reading!

Allow me to explain, when you put your probes across the zener diode of 2.4 volt using the times 10 k ohm scale, 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 checking and the pointer point to the 0 ohm scale then the zener diode is consider to have shorted reading. When you measure a 6.1 v zener diode, as usual one way will point to zero ohms while the other way will show a higher resistance which is in the 25 to 60 ohms. As you measure a higher voltage of a zener diode the resistance will gradually increase. These are the characteristic of a known good working zener diode.

When you check a zener diode from 13 v 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 have any reading otherwise it is shorted. Start taking out zener diode from your component's rack and perform some testing, compare a known good zener diode with a shorted one. It would'nt take you a long time to become familiar 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. For example you can substitute a 18v 1watt zener diode to a 18v 1/2watt zener diode.