Service manual

STP 11-25R13-SM-TG
N - 2
N-2. Diode Front-to-Back Ratio Check.
A multimeter can be used as an ohmmeter to check the condition of a solid-state diode. Check the
resistance ratio. Diodes must have a reverse-to-forward resistance ratio of at least 10:1. This means
that a diode's reverse-bias resistance must be at least 10 times as great as its forward-bias resistance
(Figure N-2).
Figure N-2. Resistance Ratio (Good/Bad)
N-3. Malfunctions.
a. If a diode is open, the ohmmeter will indicate infinity (high resistance) in both directions as it
does for any open.
b. If a diode shorts, the ohmmeter will show zero (low) resistance both ways. In some cases, a
diode will indicate a fixed resistance that is the same in both directions.