A Zener diode is like a one way check valve,with a twist. Unlike a regular diode that is just a on way check valve the Zener is also a voltage regulator. What ever the preset voltage is, that is the regulated voltage that will be allowed to pass through. If hooked up in the other direction then the check valve part of the diode comes into play, no voltage gets through.
I realize this is a simplified explanation and more factors come into play. But for the most part this is what they do.
Thats why if there is more than one Zener stored in the same place and they are not marked as to what voltage they are. It is impossible to know.
So, if this the case for you then you need a Zener diode checker.
To operate this checker is very simple. You put the Zener on the checking lugs that have the magnets. Hook up the power on the back lugs. Turn on the power to the back lugs. Turn sw on on the checker. Adjust pot to get the highest voltage on the meter. That is your Zener voltage.
I do not have pic's from the start of this build. It was started before i joined Instructables. So these build pics are just the last part.
Step 1: The schematic
I think the first checker was affected by the charging and discharging of the cap. Made it difficult to get a steady readout. I am not really sure but it was hard for me to use.
The hand drawn schematics are just from my reference book that i use. They are the same as the previous 2 schematics.