Electronics > Beginners
MELF Diode with Colour Ring
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2X:
Hello, I measure the below diode and it is short circuit at forward and reverse polarity. Does anyone knows what diode is in order to replece the old one?

jmelson:
Z3 makes me think it must be a Zener diode.  Can't help more than that.

Jon
bob91343:
If it shows short in both directions, it's bad and should be replaced.
2X:
The problem is that I didn't know which is the breakdown voltage (if it is zener diode).
MagicSmoker:
The color band code for MELF zener diodes is not standardized, but it looks like Z2 has the same band so if it is ok then you can apply a current-limited variable voltage across it to determine the breakdown voltage. Basically, insert a 10k resistor in series with the positive terminal of an external power supply (ideally a variable one) and measure the voltage across Z2 when this current-limited voltage is applied. If you connect positive to cathode then the voltage will clamp at the zener voltage (+/- a few %); if you connect it positive to anode then it will clamp at 0.6-0.7V.

(mini rant: this is also an excellent object lesson in why you should never use MELF package parts!)

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