An electronics technician performs diagnostic checks on various malfunctioning direct-curr… — Armed Services Vocational Aptitude Battery (ASVAB)

An electronics technician performs diagnostic checks on various malfunctioning direct-current (DC) systems. Match each electrical troubleshooting symptom or meter reading on the left with its most probable circuit fault condition on the right.

An ohmmeter test across a de-energized relay coil rated at $250\,\Omega$ measures $0.0\,\Omega$ .Short-circuited (shorted) coil windings
A voltmeter measures full source voltage ( $12\text{ V}$ ) directly across the terminals of a closed switch in an active, non-functioning circuit.Open circuit caused by failed or pitted switch contacts
A circuit displays normal source voltage under no-load conditions, but voltage at the load drops drastically below specification when operating under full current draw.High-resistance connection or corroded terminal
An ohmmeter connected between an isolated appliance's ungrounded positive power lead and its metallic chassis reads $0.0\,\Omega$ .Direct ground fault (short to chassis ground)

Cevap

The symptom of 0.0 ohms across a 250-ohm coil matches short-circuited coil windings; full source voltage measured across closed switch terminals matches an open circuit from failed switch contacts; voltage dropping severely under load matches a high-resistance or corroded connection; and 0.0 ohms between the ungrounded positive lead and metallic chassis matches a direct ground fault.

Each diagnostic reading correlates directly to fundamental circuit failure modes: a shorted coil eliminates component resistance (

0\,\Omega

); an open switch drops the entire source voltage (

12\text{ V}

) because current cannot bridge the open gap; a high-resistance joint creates excessive voltage drop only when current flows (

V = I \times R

); and continuity between a 'hot' power lead and the chassis represents a short to ground.

Adım Adım Çözüm

Analyze the relay coil resistance reading of

0.0\,\Omega

Identifies an internal short circuit.

Inductive components such as relay coils are designed with specific continuous wire resistance. A reading of

0.0\,\Omega

means the insulation between windings broke down, creating a direct short.

Analyze the closed switch voltage reading showing full source voltage.

Identifies an open switch fault.

According to Kirchhoff's Voltage Law, an open point in a series circuit drops the entire source voltage because it creates infinite resistance and blocks current, whereas a properly closed switch drops

0\text{ V}

Analyze the loaded vs. unloaded voltage drop behavior.

Identifies a high-resistance connection fault.

When no current flows (

I = 0

), no voltage is dropped across bad connections (

V = 0\text{ V}

). When load current flows, parasitic resistance drops voltage in proportion to current, starving the load.

Analyze the zero-ohm reading between the positive supply rail and metal chassis.

Identifies a direct chassis ground fault.

Conductors intended to carry current must remain insulated from the metal chassis. A

0.0\,\Omega

reading confirms an unintended low-resistance bridge to the chassis frame.

Anahtar Kavram

Circuit fault diagnosis using voltage drop and resistance characteristics for opens, shorts, grounds, and high-resistance faults.

Tahmini Süre:1m 30s

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