Forward Voltage Drop (Vf) * Volts (V)

Reverse Voltage (Vr) * Volts (V) - OL = Open

Diode Type Material type

Good Silicon: 0.7V, OL Good Schottky: 0.25V, OL Faulty: 0V forward, 0V reverse Faulty: Leaky reverse

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Verdict

Diode

How to test a diode: Set multimeter to diode mode. Forward bias: Red probe on anode, black on cathode. Reverse bias: Swap probes. Good diode shows Vf (0.6-0.8V) forward, OL reverse.

Zener Voltage Reading * Volts (V)

Rated Zener Voltage Volts (V)

Reverse Leakage (Vr) Volts (V) - OL = Open

Good Zener: 5.1V, OL Faulty: Low Vz Faulty: Short circuit

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Verdict

Zener

How to test a Zener diode: Set multimeter to diode mode. Forward bias: 0.6-0.8V. Reverse bias: Should show the Zener voltage (e.g., 5.1V). If it shows OL or 0V, it's faulty.

B-E Voltage (Vbe) * Volts (V)

B-C Voltage (Vbc) * Volts (V)

C-E Leakage Volts (V) - OL = Open

Transistor Type Type

Good NPN: Vbe=0.7, Vbc=0.7, OL Faulty: B-C short Faulty: All shorted

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Verdict

Transistor

How to test a transistor: NPN: Base positive, emitter negative. Vbe and Vbc should be ~0.7V. PNP: Base negative, emitter positive. Vbe and Vbc should be ~0.7V. C-E should show OL (open circuit).

Input Voltage (Vin) * Volts (V)

Output Voltage (Vout) * Volts (V)

Rated Output Volts (V)

Dropout Voltage Volts (V)

Good 7805: 12V in, 5V out Faulty: Output = Input (shorted) Faulty: No output (open) Faulty: Vin too low

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Verdict

Regulator

How to test a voltage regulator: Apply input voltage (must be > Vout + dropout). Measure output voltage. Good regulator: Vout is within ±5% of rated voltage.