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I am sorry if the title is misleading. As I am not a native speaker, I really don't know what the correct words to be used in the title. If you know the right words, please tell me so I can update the title.

My question is about a repair test named "reverse conduction test". I don't know the right name in english but its a literal translation from my idiom to english. "Reverse conduction test" is a test made by people who repair computers and smartphones' motherboard (and probably it applies to any other kind of circuit). It uses the diode mode test of a multimeter but on a different way.

These are the steps:

  • take the red probe and place it on ground.
  • take the black probe and place it on the pin you want to measure

This is going to give a reading on the multimeter's display. This value is then compared to a reference value. When the values differs, then probably there is an error on that pin/trace/region.

This video https://www.youtube.com/watch?v=pRpyHF2dfq0 shows someone using the diode mode to measure the values.

Here are my questions:

  1. what's the correct name of this test in english?
  2. How does it work? I don't understand how the red and black probes are inverted and still can read a voltage drop in a trace that probably contains PN junctions reversed.
  3. Why this test uses red and black probe swapped? Is there a a technical explanation for this?
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  • \$\begingroup\$ It seems like the key word here is "polarity." (Reverse polarity test.) \$\endgroup\$
    – JYelton
    May 16 at 20:40
  • \$\begingroup\$ I am sorry. I really don't know. Searching for reverse polarity test return links about testing AC circuits and DC motors that doesn't seem to be the same technique used on motherboard repair videos \$\endgroup\$ May 16 at 20:45
  • \$\begingroup\$ maybe the term is reverse bias test or reverse continuity test \$\endgroup\$
    – jsotola
    May 16 at 20:55
  • \$\begingroup\$ The test is looking for unwanted current paths (i.e. short circuits, or near shorts). It's not looking for incorrectly biased diodes. It's kind of a lame test in that it's not very scientific and definitely not rigorous - It's just giving you a rough idea of where a problem might be. Basically it's better than just randomly replacing components, but not much better... \$\endgroup\$
    – Kyle B
    May 16 at 21:27
  • \$\begingroup\$ They're measuring the voltage drop of the protection diodes on each input. The protection diodes conduct when reversed polarity is applied, so you have to reverse the polarity of the multimeter leads (positive to ground, negative to signal). See this question for more information: electronics.stackexchange.com/questions/366143/… \$\endgroup\$ May 17 at 0:08

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