Fault Finding, Repair and Measurement - Berufsbildung ·...

Released_task_FaultFinding_RepairAndMeasurement

Fault Finding, Repair and Measurement

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Contents The following are the documentation for this Project: WSC2013_TP16_SG_FFM.pdf Test Project Document WSC2013_TP16_SG_SCH.pdf Fault Finding Schematics (3 sheets) WSC2013_TP16_SG_CMP.pdf Fault Finding Component Layout WSC2013_TP16_SG_PCB.pdf Fault Finding PCB Design Datasheet Document PDF Data Files Introduction

This project is a FM Stereo Test Transmitter. It generates the necessary signals to test FM Stereo Receivers and Stereo Decoders.

Fig. 1: Audio Signals, Sub-Carrier and Multiplexed (MPX) Signals

Instead of using special purpose ICs to produce the waveforms this design uses ordinary HCMOS logic. Audio Frequency (AF) signals are produced using binary counters and combinational logic and then filtered to obtain two very low distortion sine waves to serve as the test tones. These audio signals are then multiplexed by a 38kHz Sub-Carrier to form a Left+Right and a Left-Right Double Side-Band Suppressed Carrier (DSBSC) signal to form the Stereo Multiplex (MPX), Fig 1. A 19kHz signal is added to the MPX as a Pilot Tone. This can be used to test FM stereo decoders or FM modulated for testing FM stereo receivers. The frequency modulation (FM) oscillator is free running at 65MHz (reduced from 88~108MHz due to bandwidth limitation of the supplied oscilloscope) and can be finely adjusted over + 300kHz with the variable capacitor.


Description of the Project The block diagram of the FM Stereo Test Transmitter is shown in Fig. 2.

Fig. 2: Block Diagram of FM Stereo Test Transmitter

The Signal Generator generates the 38kHz sub-carrier and 19kHz pilot tone. It uses an ingenious technique to generate 2 sine waves (audio) with very low distortion at around 300Hz and 1.2kHz after being filtered with what is effectively a 3-pole Sallen-Key Low-Pass Filter. Before filtering the digital waveform has a fourier series as follows:

8

√2.

77

99

1515

1717

2323

⋯

The 38kHz sub-carrier is used to multiplex the audio signals and then summed with the 19kHz pilot by the Multiplexer & Summer to form 16 different waveforms (Fig 3). The audio signals being encoded as Left or Right is based on the phase of the sub-carrier. The 16 different waveforms are:

300Hz Mono Audio Only 300Hz Left Only MPX, No 19kHz Pilot

1.2kHz Mono Audio Only 300Hz Left Only MPX, with 19kHz Pilot

300Hz + 1.2kHz Mono Audio Only 300Hz Right Only MPX, No 19kHz Pilot

19kHz Pilot Only 300Hz Right Only MPX, with 19kHz Pilot

300Hz Left/1.2kHz Right MPX, No 19kHz Pilot 1.2kHz Left Only MPX, No 19kHz Pilot

300Hz Left/1.2kHz Right MPX, with 19kHz Pilot 1.2kHz Left Only MPX, with 19kHz Pilot

300Hz Right/1.2kHz Left MPX, No 19kHz Pilot 1.2kHz Right Only MPX, No 19kHz Pilot

300Hz Right/1.2kHz Left MPX, with19kHz Pilot 1.2kHz Right Only MPX, with 19kHz Pilot

Fig 3: Multiplexer and Summer Outputs

Manual/ Auto Clock

Control Logic

Multiplexer &

Summer

FM Modulator

FM Modulated Output

MPX Output

Signal

Generator

Audio 19kHz 38kHz


The following are 2 waveforms that can be expected:

Fig 4: 300Hz Right/1.2kHz Left MPX, No 19kHz Pilot

U12: QA=0, QB=0, QC=0, QD=0

Fig 5: 300Hz Right/1.2kHz Left MPX, with 19kHz Pilot

U12: QA=1, QB=0, QC=0, QD=0 The control signals from the Control Logic controls the switching and summing and therefore the output waveforms of the Multiplexer & Summer. The state of the Control Logic is advanced by the Manual/Auto Clock. In manual mode the advancing is done by a Push Button via a de-bouncing circuit. In Auto mode it is advanced every 3 seconds. Jumper J1 is the power connection to the FM Modulator. Put the jumper to the OFF position when not working on that section of the circuit. Jumper J2 selects the mode of advancing the state of the Control Logic, Manual or Auto. Jumper J3 directs the MPX signal to the FM Modulator (To Mod) or to H2 (To H2).


Instructions to the Competitor

Fault Finding and Repair

You will have to locate and repair 6 faults in the test project. Supply voltage of 5.0 + 0.1 volts to be applied to terminal H1, please take note of the polarity. Adjust VR1 to set the frequency of the clock output at U1 Pin 3. Adjust VR2 for maximum MPX output at H2. Adjust VR101 to set the period of the clock at U101 Pin 3 to 3.0 + 0.05 seconds. When a fault is located, complete the table in the answer script (Page 11) with the component’s designator and the fault symbol. The fault symbol should be from the Fault Symbol Table (Fig 6). If the fault requires a component change, please request a component from the experts. Indicate the component requested in the Parts List and must be signed by both Competitor and Expert. You’ll need to show evidence of locating and repairing the fault by measuring and recoding up to 2 measurements prior to and after repairing the fault. Fault Symbols:

Fault Symbol Description Fault Symbol Description

Open

(part, wire or PCB trace)

Stuck at high voltage

(pin, input, output, etc)

Short

(part, wire or PCB trace)

Stuck at low voltage

(pin, input, output, etc)

Part with larger value (resistor, capacitor, etc)

? Incorrect part number or

wiring connecting

Part with smaller value (resistor, capacitor, etc)

+/- Wrong Polarity

Fig 6: Fault Symbol Table


Instructions to the Competitor (Continued)

Measurement

Before proceeding to the measurement portion of the test project, ensure that all faulty components have been replaced. You are to work with conventional testing and measurement equipment. You are to record and analyse the measured results. For each measurement, you must provide a schematic showing how you performed the measurement. Ensure that your recorded measurements have all the necessary labels, e.g. frequency, voltage, time, etc. You can use the following equipment symbols and example for the measurement schematic:

Equipment Symbol

Power Supply

Voltmeter

Ammeter

Oscilloscope

Function Generator

Fig 7: Equipment Symbol Table

Fig 7a: Example of Measurement Schematic

V

A

FG

CH1 CH2 GND

Vcc

TP1

TP2

5V


Part List

S/N Description Value Designator Qty Competitor Request

Competitor Signature

Expert Signature

1 Capacitor, Ceramic 150p C1 1

2 Capacitor, Ceramic 100n C2, C4, C9, C13, C21, C30, C32, C102, C103

9*

3 Capacitor, Polyester 22n C3 1

4 Capacitor, Ceramic 1n C5, C7, C33, C35, C39

5

5 Capacitor, Polyester 4n7 C6 1


7 Capacitor, Electrolytic

47u C10, C12 2

8 Capacitor, Ceramic 68p C11, C34 2

9 Capacitor, Ceramic 330n C20 1

10 Capacitor, Tantalum 2u2 C22 1

11 Capacitor, Tantalum 680n C23 1

12 Capacitor, Electrolytic

220u C31 1



15 Capacitor, Variable 2~22p C38 1

16 Capacitor, Tantalum 3u3 C101 1

17 Diode, Variable Capacitance

BB208-03 D1, D2 2

18 Inductor, Wire Wound

Inductor L1 1

19 LED, Red, T1-¾ LED LED1 1

20 Resistor, Axial, ¼ W 820R R0 1

21 Resistor, Axial, ¼ W 13k R1 1


23 Resistor, Axial, ¼ W 390k R3, R101, R102 3


25 Resistor, Axial, ¼ W 1k8 R5, R11 2



28 Resistor, Axial, ¼ W 2k7 R8 1

*Decoupling Capacitors C41~C56 not included in parts list


S/N Description Value Designator Qty Competitor Request

Competitor Signature

Expert Signature





33 Resistor, Axial, ¼ W 330k R14, R15 2

34 Resistor, Axial, ¼ W 12k R16, R17, R20, R21, R22, R24

6

35 Resistor, Axial, ¼ W 4k7 R18, R35 2



38 Resistor, Axial, ¼ W 22k R30, R32 2







45 Switch, Push Button SW-PB S1 1

46 Transistor, NPN, RF BF199 T1 1

47 Timer IC TLC555CP U1, U11, U101 3

48 12-Bit Binary Counter

SN74HC4040N U2 1

49 Quad 2-Input Ex-OR Gate

SN74HC86N U3, U4, U5 3

50 Precision Dual Op Amp

TLC277CP U6, U7 2

51 Quad Bilateral Analog Switch

SN74HC4066N U8 1

52 Quad 2-Input OR Gate

SN74HC32N U9 1

53 Quad 2-Input AND Gate

SN74HC08N U10, U16 2

54 4-Bit Binary Counter 74HC93N U12 1

55 Hex Inverter SN74HC04N U13 1

56 Triple 3-Input OR Gate

CD74HC4075N U14, U15 2

57 Resistor Variable 5k VR1, VR2 2

58 Resistor Variable 100k VR101 1


Fig. 8: Schematics – Sheet 1




Fig. 11: Component Layout Overlay


Fig. 12: Top Layer

Fig. 13: Bottom Layer (Bottom View)


Fault Finding & Repair – Answer Script Defective Part Fault Symbol

Fault #1

Before After

Measurement #1

Node:_______

Measurement #2

(Optional)

Node:_______

Defective Part Fault Symbol

Fault #2

Before After

Measurement #1

Node:_______

Measurement #2

(Optional)

Node:_______



Fault #3

Before After

Measurement #1

Node:_______

Measurement #2

(Optional)

Node:_______


Fault #4

Before After

Measurement #1

Node:_______

Measurement #2

(Optional)

Node:_______



Fault #5

Before After

Measurement #1

Node:_______

Measurement #2

(Optional)

Node:_______


Fault #6

Before After

Measurement #1

Node:_______

Measurement #2

(Optional)

Node:_______


Measurement – Answer Script

Measurement #1

Measure and record the frequency of the two audio signals and the phase shift contributed by their corresponding low-pass filters (U6A and U6B). Measurement Schematic

Measurement Output Audio Signal #1

Vertical Settings:

/div

Horizontal Settings:

/div

Measurements:

Freq: ________ Hz

Phase: ________ deg


Audio Signal #2 Vertical Settings:

/div


/div

Measurements:

Freq: ________ Hz

Phase: ________ deg

Measurement #2 Measure and record the gain of the summing amplifier (U7A) for both audio signals. Measurement Schematic


Measurement Output Audio Signal #1

Vertical Settings:

/div


/div

Measurements:

Freq: ________ Hz

Gain: ________

Audio Signal #2

Vertical Settings:

/div


/div

Measurements:

Freq: ________ Hz

Gain: ________


Measurement #3 Measure and record the QA, QB, QC and QD outputs from U12 and the corresponding control signals U, V, W, X, Y and Z. Use the grid on the next page to record these measurements. Measurement Schematic


Measurement Output

QA

QB

QC

QD

U

V

W

X

Y

Z


Measurement #4 Measure and record the measurement(s) that best represent the Left-Right Double Side-Band Supressed Carrier (DSBSC) signal of the test project. Measurement Schematic

Measurement Output

Vertical Settings:

/div


/div

U12 QA = _______

U12 QB = _______

U12 QC = _______

U12 QD = _______


Measurement #5 Measure the “1.2kHz Left Only MPX, No 19kHz Pilot” and ”1.2kHz Right Only MPX, No 19kHz Pilot” waveforms showing the difference between them. Also indicate the corresponding QA, QB, QC and QD outputs of U12. Measurement Schematic

Measurement Output

1.2kHz Left Only MPX, No 19kHz Pilot Vertical Settings:

/div


/div

U12 QA = _______

U12 QB = _______

U12 QC = _______

U12 QD = _______


1.2kHz Right Only MPX, No 19kHz Pilot

Vertical Settings:

/div


/div

U12 QA = _______

U12 QB = _______

U12 QC = _______

U12 QD = _______

Complete the table below for the other waveforms. Two of them have already been filled in based on Fig. 4 and Fig 5.

Waveform Description

U12 Outputs

QD QC QB QA

300Hz Mono Audio Only

1.2kHz Mono Audio Only

300Hz + 1.2kHz Mono Audio Only

19kHz Pilot Only

300Hz Left/1.2kHz Right MPX, No 19kHz Pilot

300Hz Left/1.2kHz Right MPX, with 19kHz Pilot

300Hz Right/1.2kHz Left MPX, No 19kHz Pilot 0 0 0 0

300Hz Right/1.2kHz Left MPX, with19kHz Pilot 0 0 0 1

300Hz Left Only MPX, No 19kHz Pilot

300Hz Left Only MPX, with 19kHz Pilot

300Hz Right Only MPX, No 19kHz Pilot

300Hz Right Only MPX, with 19kHz Pilot

1.2kHz Left Only MPX, No 19kHz Pilot

1.2kHz Left Only MPX, with 19kHz Pilot

1.2kHz Right Only MPX, No 19kHz Pilot

1.2kHz Right Only MPX, with 19kHz Pilot


Marking Scheme

Max Mark Aspect of Criterion - Description

1.75 Fault #1 + Evidence






2.0 Repair of Faults as per IDC-A-610-D

2.5 Measurement & Documentation #1





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