Should be so simple... 3 LED's powered via 9v battery

Jan 8, 2011 at 11:39 AM Post #31 of 31
If the LED is working you should see a drop of 1.3 volts across it.
Place your negative probe at the bottom of the string, place the
positive probe on the other side of the first LED. You should see 1.3 volts.
Now, move the positive probe one LED up the string. Now you should see
2.6 volts. Move the positive probe up to the last LED and you should see
3.9 volts. If one of the LED's has no voltage drop and the others do, then
that LED is shorted. If the only voltage drop you get is 9 volts then the
string is open or an LED is backwards. Your resistor calculation is correct.
 

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