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Old 15th April 2012, 07:56 PM   #1
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Default diode 3 9

hi all

I removed a shorted diode from a car amplifer with the marking 3 9 0n it.The symbol on the board is the zener symbol.I remove another one with the same marking and put in series with a 1 k resistor and apply 24v dc to it.I did not get any voltage droup across the diode.Is this just an ordinary diode?
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Old 16th April 2012, 09:42 PM   #2
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Quote:
Originally Posted by ian33 View Post
hi all

I removed a shorted diode from a car amplifer with the marking 3 9 0n it.The symbol on the board is the zener symbol.I remove another one with the same marking and put in series with a 1 k resistor and apply 24v dc to it.I did not get any voltage droup across the diode.Is this just an ordinary diode?

Even an 'ordinary' diode will have some voltage drop when forward biased - usually around 0.6 - 0.7VDC. The same goes for a zener diode when forward biased. The zener voltage is obtained when the zener is reverse biased. So perhaps you did not apply enough voltage to get to the reverse bias point of the zener. Try a higher voltage and see if you get different results.
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Old 16th April 2012, 09:52 PM   #3
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It is possible that you set the diode in the wrong direction. The band of the zener diode goes to the voltage and the other side to ground. If you reverse it you get about .5 volts. Try it again and make sure the band goes to the volatge.
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Old 16th April 2012, 09:58 PM   #4
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It could be the symbol for a TransZorb, which is similar. E
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Old 17th April 2012, 02:15 AM   #5
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I tried it again and got 0.7v so i guess it is not a zener.
The voltage across this diode when it is on the board is 14.02v
so i think 24v was enouth to apply to it to get a voltage droup
if it was a zener?
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Old 17th April 2012, 02:23 PM   #6
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Zener is .6-.7V forwards (plus on blank end), zener voltage backwards (plus to line). Current through 1k might blow a tiny zener with 24v behind it, I'd use 10k . Zeners tend to be grey or brown, transient absorbers tend to be blue or green. Some series have the voltage printed on them, 3 9 might be 3.9v.
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