Logic Probes for IC Failure Detection

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Questions and Answers

What is the relationship between the peak voltage VM and the RMS voltage VRMS for a sine or cosine wave?

VRMS = 1.414 VM

VRMS = VM/0.707

VRMS = 0.707 VM (correct)

VRMS = 2 VM

What is the main purpose of a decade box?

To generate AC signals

For load substitution (correct)

To measure voltage

To amplify weak signals

What is the significance of the number of sections (dials) on a decade box?

It determines the accuracy of the measurement

It determines the type of component (resistance, capacitance, or inductance)

It determines the maximum voltage it can handle

It determines the range of values that can be set (correct)

What type of waveforms is the formula VRMS = 0.707 VM applicable to?

Sine or cosine waves Signup and view all the answers

What is the purpose of the selector switch on a decade box?

To set the desired value within the range of the box Signup and view all the answers

What is the significance of the symmetry line CD on the oscilloscope?

It represents the zero voltage reference Signup and view all the answers

What is the name of the device used to accurately set resistance, capacitance, or inductance values?

Decade box Signup and view all the answers

What type of decade boxes are available?

Resistance, capacitance, and inductance types Signup and view all the answers

What is the minimum pulse width that some logic probes can detect?

10 ns Signup and view all the answers

How do most IC failures typically show up in a circuit?

As a constant high or low level Signup and view all the answers

What is the advantage of using a logic probe over an oscilloscope?

It can detect high-speed transient pulses Signup and view all the answers

What is the purpose of connecting the croc clip to the 0-V rail in a basic logic probe?

To check the logic levels during logic gate experiments Signup and view all the answers

What happens when both LEDs turn on dimly in a basic logic probe?

A high-frequency pulse train is being detected Signup and view all the answers

What is the function of an oscilloscope?

To measure the voltage and frequency of an electrical signal Signup and view all the answers

How are pins 7, 8, 9, 12, and 13 of the CD4011 IC connected in the basic logic probe circuit?

To the negative supply rail Signup and view all the answers

What is the advantage of using a logic probe in conjunction with an oscilloscope?

It can detect high-speed transient pulses that are hard to detect on an oscilloscope Signup and view all the answers

What can be determined by comparing the amplitude of the reflected step in a time-domain reflectometer?

Both the distance to and the nature of the fault Signup and view all the answers

What can be revealed by time-domain reflectometry?

Both the distance to and the nature of the fault, as well as the characteristic impedance of the line Signup and view all the answers

What is the primary function of the IFR NAV-402AP Nav/Comm Test Set?

To test and calibrate MKR, VOR, ILS, and COM avionics Signup and view all the answers

What feature does the IFR NAV-402AP offer for VOR testing?

A VOR bearing selectable in 0.1° steps Signup and view all the answers

What type of frequency modes are available in the IFR NAV-402AP signal generator?

Both XTAL and VAR frequency modes Signup and view all the answers

What is the purpose of the sweep LOC DDM function in the IFR NAV-402AP?

To test autopilot capture mode Signup and view all the answers

What type of tester is the IFR NAV-402AP designed to be used as?

Both a bench and ramp tester Signup and view all the answers

What avionics systems can be functionally tested and calibrated using the IFR NAV-402AP?

MKR, VOR, ILS, and COM avionics Signup and view all the answers

What is the primary function of the oscillator stage in an RF signal generator?

To accurately set the signal frequency Signup and view all the answers

What type of circuit is used in low-frequency signal generators to produce the correct range of resonant frequencies?

LC circuit Signup and view all the answers

What is the purpose of the modulating circuit in an RF signal generator?

To produce an audio or video voltage Signup and view all the answers

What type of modulation is used in specialized signal generators that allow for pulse modulation?

Pulse modulation Signup and view all the answers

What does the output-level meter in an RF signal generator indicate and control?

The output voltage of the generator Signup and view all the answers

What is the range of output readings indicated by the output-level meter in an RF signal generator?

Tenths through the value of 1.0 Signup and view all the answers

What is the purpose of the calibrated attenuator in an RF signal generator?

Not specified in the text Signup and view all the answers

What is the typical source of the modulating signal in an RF signal generator?

Either of the above Signup and view all the answers

What is one of the functions of an FQI test set when used with a capacitance-type fuel gauging system?

Measures insulation resistance of tank units and cabling Signup and view all the answers

What is the purpose of introducing adequate capacitance in an FQI test set?

To simulate the function of the compensator Signup and view all the answers

What is a potential hazard when using an FQI test set?

Fire due to sparks Signup and view all the answers

What does loop resistance testing analyze in cables?

The resistance at two locations of interest within a loop Signup and view all the answers

What is the primary cause of corrosion in electrical ground paths?

Chemical reactions with air Signup and view all the answers

What is the result of corrosion in electrical ground paths?

Increased resistance Signup and view all the answers

What is the purpose of ensuring correct earthing of the test box when using an FQI test set?

To prevent sparks and fires Signup and view all the answers

What is the typical power source for FQI test sets?

115 V AC at 400 Hz Signup and view all the answers

Study Notes

Logic Probes

Detect and display high-speed transient pulses as small as 10 ns wide
Connected directly to the power supply of the device being tested, or have internal batteries
Provide a quick, inexpensive way of locating faults in IC failures
Can display single, short-duration pulses that are hard to detect on an oscilloscope

Basic Logic Probe

Can be used to check logic levels during logic gate experiments
Red LED turns on if the level is high, green LED turns on if the level is low
If both LEDs turn on dimly, a high-frequency pulse train is being detected

Oscilloscopes

A sophisticated voltmeter with a two-dimensional graph display
Used to measure voltage (amplitude) and frequency (time) of an electrical signal
The peak or maximum voltage seen on the scope face is VM volts
Vrms = 0.707 VM (for a sine or cosine wave)

Decade Boxes

An assembly of precision resistors, coils, or capacitors
Can be set to any desired value within its range
Used for load substitution
Types available: resistance, capacitance, and inductance

Decade Resistance Boxes

Each switch section represents a decade, or a multiple of 10
Can be set to any desired value within its range

Signal Generators

Produce a signal that can be accurately set in frequency at any point in the range
The oscillator stage produces a signal which can be accurately set in frequency
The modulating circuit produces audio (or video) voltage which can be superimposed on the RF signal
Modulation types: sine wave, square wave, pulse modulation

Time-Domain Reflectometer (TDR)

Measures the distance to a fault as well as the nature of the fault
Indicates the characteristic impedance of the line and whether losses are shunt or series
Used to locate and analyze connectors and splices

IFR NAV-402AP Nav/Comm Test Set

A self-contained unit for functional testing and calibration of MKR, VOR, ILS, and COM avionics
Can be used both as a bench and ramp tester
Features: signal generator, VOR bearing, LOC-G/S output, sweep LOC DDM

Fuel Quantity Indicator (FQI) Test Sets

Used to measure capacitance values of individual or sets of tank units
Inserts appropriate capacitance values of a fuel gauge circuit for functional calibration
Introduces adequate capacitance to simulate the function of the compensator
Measures insulation resistance of tank units and cabling

Loop Resistance Testers

Analyze circuits of cables by measuring and recording the resistance at two locations within a loop
Used to detect corrosion in electrical ground paths

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Description

Learn about logic probes that detect high-speed transient pulses and locate faults in IC circuits. Understand how they work and their advantages in debugging.