Electronic Fault Finding Unit 60 (Analogue Section)

Scenario

PASS

You are employed as a junior electronics technician in a local company which specializes in audio electronics. As a part of a major business review, senior management has decided to upgrade one of their best selling product lines.

The product to be upgraded is a mono amplifier which can be used for a variety of purposes including playing an IPOD. The previous product had suffered from a number of small design flaws which the manufacturing department had found difficult to trace and fix. As a part of an ongoing drive to improve quality, senior management have tasked you to produce a handbook for the new product explaining:

  • The circuit function
  • A fault location strategy for the amplifier
  • Identification of correct input and output signals

MERIT

Furthermore you are tasked to present your findings to a panel. As a part of this presentation you have been strongly advised to include the following:

  • An alternative circuit which accomplishes the same thing
  • A full evaluation of the fault finding strategy you have selected
  • A justification for the selection of test instruments used for fault location with this circuit

DISTINCTION

To complete your presentation you have been asked to build and test a prototype circuit which can be used to:

  • Identify correct input and output signals
  • Identify signals that fall outside the expected parameters of operation
  • Show how a fault conditions in one circuit can affect the operation of the overall product

Pass Section

Read a circuit diagram for an electronic system and identify two different types of analog circuit, the components that make up each circuit and the input and output signals.

P1

The circuit shown above has had certain areas of interest outlined by numbered green boxes. For each of the green boxes you need to:

  1. Identify the components within the box
  2. Briefly explain the function of the circuit within the box
  3. Explain the type and size of voltage signal you would expect to measure at the input and output of boxes 1, 3 and 4
  4. Briefly explain how the entire circuit functions from input to output

P3

As a fully trained electronics technician you are aware that there are a number of fault location strategies which could be used to trace faults within this circuit. Select and prepare a fault location strategy using with regard to the following list:

  • Planning (block diagrams, schematics)
  • Component tolerances
  • Circuit specifications (maximum input signal, maximum output signal for example)
  • Circuit parameters (maximum power output as an example)
  • Identification of key nodes/signal test points
  • A test schedule (how often should the circuit be examined during the testing and production cycle)

P5/Distinction

Select and use test instruments to demonstrate how a faulty or incorrectly selected component can cause fault conditions within the amplifier circuit. You will need to do this as a part of your presentation for the pass outcome. The distinction will require a full evaluation of the process. You should select three different types of fault and use three of the strategies listed below to show how the fault was identified:

  • Input to output/output to input
  • Half split method
  • Symptom to cause hierarchies
  • Unit substitution
  • Visual inspection
  • Trouble shooting charts
  • Component data sheets
  • Operation and maintenance manuals

P7

Record the test data from your presentation for P5, for example:

  • Input signals
  • Output signals
  • Power supply voltage
  • DC levels at points in the circuit
  • Signal distortion
  • Signal clipping
  • Gain
  • Power consumption
  • Current
  • Resistance

Produce a test report on the fault location exercise.