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Zener diode question

Discussion in 'General Technical Questions and Answers' started by WF7A, Jun 20, 2019.

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  1. KA9JLM

    KA9JLM Ham Member QRZ Page

    I recommend not buying anything that AA7EJ worked on.
    AC0OB, KS4W, KA1SHU and 2 others like this.
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    Wrong. A zener and other types normally do go short.

    You can measure the voltage across a Zener to see if it is good.

    They do go open when you install a bigger fuse or install backwards. Then they pop like a firecracker.
    Last edited: Jun 20, 2019
    KS4W likes this.
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The standard failure mechanism for all P-N junction devices is a short circuit, or close to one.

    The only time they can fail "open" is from a current surge containing so much energy it blows the contacts off the die. But normal heating from excessive dissipation or thermal runaway causes the silicon to become extremely leaky and ultimately a near short-circuit.
    K2XT, KA9JLM and K7JEM like this.
  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    Yes. Exactly. Shirley has us both on ignore, He will never learn the facts. o_O
    Last edited: Jun 20, 2019
  5. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    51 cents now? It keeps going up every other week... I've lost track.

    With some pieces of consumer equipment, it's easier to throw it out than to extract the board (been there, done that). If it can be fixed with a diode or resistor, just keep the heat down and hope the connection underneath stays good. :p

    ... and then throw it out... :oops:
    KA9JLM likes this.
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    It is best to use a clip on heat sink near the board to do that. It does work.

    I use my shotgun as a last resort.
    KD2ACO likes this.
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Shotgun = dangerous.

    I use a sledge hammer and have a 16-lb one that does most jobs well.:)
    WQ4G likes this.
  8. WR2E

    WR2E Ham Member QRZ Page

    The shards of plastic that ensue are dangerous too!

    Wear your safety glasses!
    KA9JLM likes this.
  9. AA7EJ

    AA7EJ Ham Member QRZ Page

    Respectfully disagree - overloaded current carrying device will burn-out - open - before it will short.
    If it does short there will be other damage somewhere else - at best blown fuse etc.
    Since we are assuming it is a Zener - they have both voltage and CURRENT ( wattage) spec.
    If it is indeed open and it looks from video as "SMALL" (current) Zener replacing it with same current (wattage) rating is dubious.
  10. K7JEM

    K7JEM Ham Member QRZ Page

    You obviously have not replaced many failed diodes. They almost always fail shorted, like 95% of the time. Regular diodes and zeners both fail this way, transistors fail in a similar manner, usually a CE short. After failure of a zener it is always good practice to check the resistor that supplies current to the zener to make sure it has not failed "open".
    WQ4G, KD2ACO and KA9JLM like this.

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