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Using the 87V DMM diode-test on LEDs

By Tom Lange

August 2005

I am an Electronics Tech for the Sheboygan Area School District, Sheboygan WI. We recently had to troubleshoot a scoreboard that utilized numerous LED's connected in series, where part of a segment would not light. At first I thought we would have to set up a DC power source and resistor to test each LED, but I wanted to see if we could test it on our Fluke 87 Digital Multimeter in the diode-check mode first. To our pleasant surprise, we got a reading of approximately 1.6 volts and a slight glow from each working LED. The defective LED showed an ".OL" on the Fluke, and the LED would not glow. Replacing the LED brought the segment on the board back to life.