Help with Zener testing

Discussion in 'The Projects Forum' started by wanders, Feb 23, 2012.

  1. wanders

    Thread Starter New Member

    Jan 19, 2012
    10
    0
    I'm testing a suspect 25v zener diode out of circuit. My Protek 608 DMM has a dedicated zener function which claims to test zeners up to 20v. The test reads O/L in both directions. Am I safe in assuming that this is a bad part, or should I conduct additional tests?

    Thanks
     
  2. #12

    Expert

    Nov 30, 2010
    16,283
    6,795
    That thing about "both directions" seems to indicate that the part is "open" (bad). It should look like a simple diode in the forward direction. Still, trying to run 10 milliamps through it and measuring the voltage across the part is another way to do this.
     
  3. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    simple test is put your meter on diode test and check it again-dependant on which way round you connect your test leads you should have a reading one way round and oc reading the other ....you could also add a resistor in series with your zener and apply a voltage above the marked zener voltage to check if the zener works as it should
     
  4. ifixit

    Distinguished Member

    Nov 20, 2008
    638
    108
    Hi wanders,

    A zener should read like a diode in the forward direction and display the zener voltage in the reverse direction. Since yours reads like an open circuit in the forward direction then it is safe to assume the zener is blown open and is no longer zenering. :eek:

    You should investigate why the zener failed, there may be other failed parts that need replacing, or perhapes the design is dissipating too much power in the zener.

    Regards,
    Ifixit
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    he he he "no longer zenering" :) :)
     
  6. #12

    Expert

    Nov 30, 2010
    16,283
    6,795
    They do that, sometimes.
     
  7. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    To test a 20V zener you will need a voltage source greater than 20V.
    I suggest you put 24V in series with a 220-ohm resistor (or any similar value) and connect to the zener. Read the voltage across the zener with a DC voltmeter.
     
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