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[SOLVED] 0.02V voltage drop across diode??

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swordz60

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Hello,
I am working on a APC UPS faulty board and have run into a problem: 1N5819 diodes read 0.02V drop across them when tested using multimeter (the diodes are soldered in place). That is the same even if i switch polarities of the multimeter. When using continuity check it reads 20 ohm and beeps. :-| Are they bad or could something in the board be affecting the reading? Other diodes (like P600M, MUR4100) check out ok (voltage drop as excpected or shorted at both ends if bad). Thank you for answers.
 
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Shorted diode, or something else in shunt. You'd
have to lift one lead to be sure.
 
Hmm, it reads 0.17 when taken out. It reads an open circuit when polarity is changed, so it would seem the diode is ok, except for the abnormally low voltage drop :???:
 

The voltage drop isn't the diode. When you measured 0.17 and open circuit the readings were as expected for that kind of device, what you are seeing is some other component(s) across the diodes connection points which are more conductive. Without a schematic its difficult to predict what readings to expect.

Brian.
 
If it's a big rectifier then maybe wimpy DMM resistance
measurement forced current just doesn't push Vf very
far. 0.17 could be sane for a Schottky, a very large area
silicon dode, etc. Very different from 0.020V.
 
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