debeers wrote:

On 28 Mayıs, 13:10, wrote:
I have a circuit that I built years ago. Rather than just replacing a
bunch of zener diodes, is there a way to test them in circuit, without
powering on the circuit?
I know that surface mount zeners fail shorted, but they can open if
there is enough current.
Can I just do a diode check at each polarity with a DMM to detect a
bad zener?
Thanks

using a multimeter, you can check the zener diodes. first get the true
values from a good one then compare the values.
while measuring, first make the forward-biased the diot then reverse-
biased.

Yes, that is right. But you can only measure the typical Silicon-Voltage
(approx .5 to .8 Volts). Switch your Multimeter to Diode-Check (that
supllies a higher Voltage than normal Resistor-check).
In one Direction you should get overflow "1" and in the other direction
the Voltage named above. That means: The Diode is OK.
Sometimes, you will get in both directions any other Voltage or even a
shortcut. That is mostly caused by other parts connected to your Zener.

Best Way to solve this Problem: Dissolder one of the Zeners Pins and get
the right Voltage...

What you can NOT measure that way, is the real Zener-Voltage.
You would need a little Test-Circuit (and dissolder the Diode
completely).
Connect The Zeners cathode via a 10K Resistor with e.g.15V.
Ground the Anode. A Zener is only used in the "wrong direction"
The get the Voltage above the Zener. That is the real Zener Voltage.

Many Greetings from Germany,
Felix