Zener Diode Identification

[Choong]

Hi everyone, I am repairing an industrial PSU and there is a few glass
types zener diode on board and I found one which is shorted but the
problem with these small glass type zener is that it is only marked with
the numeric "123" and nothing more than that so how do I know what is
the zener voltage of this diode?

Thanks
Choong

 

[Eeyore]

Hi everyone, I am repairing an industrial PSU and there is a few glass
types zener diode on board and I found one which is shorted but the
problem with these small glass type zener is that it is only marked with
the numeric "123" and nothing more than that so how do I know what is
the zener voltage of this diode?

It sounds like you need the schematic. "123" is inadequate to identify the part.
Is that really the only marking ? Have you got a picture ?

Graham

 

[Meat Plow]

Hi everyone, I am repairing an industrial PSU and there is a few glass
types zener diode on board and I found one which is shorted but the
problem with these small glass type zener is that it is only marked with
the numeric "123" and nothing more than that so how do I know what is
the zener voltage of this diode?

Zeners are usually marked 5V1 (5.1 volts) 12V (obvious) 5.1.
123 doesn't ring a bell for me. Take a magnifying glass and a bright light
and have another look. Also, are the other zeners marked the same way? And
how did you determine they are zeners?

 

[Leonard Caillouet]

Some context on the application is needed if you can't find a schematic or
parts list. Zeners are usually used for either protection or as a
reference. What is it connected to?

Leonard

 

[AJ]

Are the other associated diodes all marked with the same identification? If
so connect one of them to a circuit using a variable voltage and current
limiting resistor. Ramping the voltage up and montioring it across the
diode, it will be obvious when you reach the zener voltage, start low then
bring the voltage up gradually.
Examine the circuit for electrolytic caps near the diodes, this may indicate
roughly what voltage range the diodes may be. As Leonard posted, some of
these are used for protection, as a crowbar device.

 

[Franc Zabkar]

Hi everyone, I am repairing an industrial PSU and there is a few glass
types zener diode on board and I found one which is shorted but the
problem with these small glass type zener is that it is only marked with
the numeric "123" and nothing more than that so how do I know what is
the zener voltage of this diode?

Thanks
Choong

Could it be 12B ???

If so, then "B" probably indicates the tolerance.

- Franc Zabkar