Zener Diode Identification

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

Choong wrote:

> 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

On Wed, 18 Jul 2007 17:49:14 +0800, Choong wrote:

> 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?

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

"Choong" <(E-Mail Removed)> wrote in message
news:469de17f$(E-Mail Removed)...
> 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

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.
"Leonard Caillouet" <(E-Mail Removed)> wrote in message
news:CJpni.502$(E-Mail Removed)...
> Some context on the application is needed if you can't find a schematic or
> parts list. Zeners are usually used for either protection or as a
> reference. What is it connected to?
>
> Leonard
>
> "Choong" <(E-Mail Removed)> wrote in message
> news:469de17f$(E-Mail Removed)...
>> 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
>
>

On Wed, 18 Jul 2007 17:49:14 +0800, Choong <(E-Mail Removed)> put
finger to keyboard and composed:

>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
--
Please remove one 'i' from my address when replying by email.