quick question re:testing diodes in circuit

Cartouche

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I'm testing all the diodes on this Atari Audio II board with my DMM. A couple of the diodes read like I expect a good diode to read, "1" (open) in one direction and a junction drop of ~5.5 in the other.

However, some of the diodes show the good junction drop but when the leads are reversed, the DMM climbs up to a reading of about 1.5-1.9. Is this common when diodes are measured in circuit? I know I can unsolder one leg and measure to be sure, but if I get a junction drop one way, is it reasonable to assume the diode is good?

I figured if a diode is bad, the DMM would indicate a short circuit...
 

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I'm testing all the diodes on this Atari Audio II board with my DMM. A couple of the diodes read like I expect a good diode to read, "1" (open) in one direction and a junction drop of ~5.5 in the other.

However, some of the diodes show the good junction drop but when the leads are reversed, the DMM climbs up to a reading of about 1.5-1.9. Is this common when diodes are measured in circuit? I know I can unsolder one leg and measure to be sure, but if I get a junction drop one way, is it reasonable to assume the diode is good?

I figured if a diode is bad, the DMM would indicate a short circuit...

If the reading is climbing, it is most likely that you are charging a capacitor somewhere in the circuit.

For best results, you need to isolate the diode and the simplest way is to unsolder one leg.

ken
 
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