Maintenance and Repair of Electronic Circuits

These flashcards cover methods, formulas, and concepts related to the maintenance, reliability, and troubleshooting of electronic circuits as described in the lecture transcript.

General Troubleshooting Process

A process involving physical observation, identifying failure symptoms, component testing, and checking input-output for each block.

Component Specifications

Data used to recognize usage, absolute maximum limits, and other important electrical data to assist in troubleshooting.

Infant Mortality

A stage of failure occurring shortly after equipment is manufactured and shipped to the customer.

Normal Failure Stage

The period where failures occur due to the working age of the equipment, typically having the lowest failure rate percentage.

Final Failure Stage

The period where an equipment experiences its highest failure rate because its working life has ended.

Partial Failure

A change in characteristics or parameters outside of specifications that does not fully eliminate the tool's overall function.

Mean Time To Fail (MTTF)

The duration of component usage until failure occurs, specifically for non-reparable electronic components.

MTTF Formula

$$MTTF = \frac{1}{FR}$$

Mean Time Between Failures (MTBF)

The duration of system usage until failure occurs, used for reparable circuits, instruments, and systems.

Circuit Failure Rate Formula

$$FR(\text{circuit}) = FR(A) + FR(B) + FR(C) + \text{...}$$

MTBF Formula

MTBF(\text{circuit}) = \frac{1}{\text{\alpha}}, where \text{\alpha} is the total circuit failure rate.

Exponential Law of Reliability

States that the probability of no system failure within time $t$ is an exponential function of that time.

Reliability (R) Formula

$R = e^{-\alpha t}$ or $R = e^{-t/m}$

Failure Probability (Q) Formula

$$Q = 1 - R = 1 - e^{-\alpha t}$$

Derating

A technique to improve reliability by operating a component below its maximum limits, such as using a $\frac{1}{2}\,W$ resistor where only $\frac{1}{4}\,W$ is required.

Redundancy

Connecting units with the same function in parallel so if one fails, the other takes over.

Active Redundancy

A standby unit that is powered on and ready to follow/replace a failure immediately, such as a UPS for a computer.

Passive Redundancy

Elements that share a load or perform functions separately but are not automatically activated, such as a manual office generator.

Symptom-function Method

A troubleshooting technique used to isolate damage to specific parts by checking basic symptoms like power cables, fuses, or switches.

Signal-tracing Method

A method used to find a specific block causing failure by tracking signals through the system.

Voltage and Resistance Method

Comparing measured data against manufacturer specifications; voltage is measured while the device is ON, and resistance is measured while it is OFF.

Half-splitting Method

A technique used for serial block circuits where the system is divided in half repeatedly until the fault is found.

Loop Breaking Method

Used for electronic systems with feedback, such as a Phase Lock Loop (PLL), by disconnecting the loop and injecting DC voltage or signals.

Substitution Method

The final stage of troubleshooting involving replacing a suspected component with a known good one using correct connections.

Failure Analysis

Used for recurring failures by analyzing circuit operation, performing measurements, and studying product data.

Signal Analysis

Using tools like a memory oscilloscope to visualize signals as clues to locate damage.

Logic Analysis

Limited to digital circuits, using one and zero signals to determine which logic function is malfunctioning through bit-per-bit testing.

Routine Diagnosis

A self-test program used in systems with at least one programmable microprocessor to perform quick internal checks.