Radio,Television And Electronic Paper 3, WASSCE (SC), 2021

Question 3

 

AIM: To test candidates’ knowledge of the components in the various stages of a television (TV) receiver.


(a)        You are provided with components A, B, C, D and E.
(b)        Identify components A, B, C and D and record in Table 2.


Table 2


Comp-onents

Name of component

Circuit symbol

Stage found in TV receiver

Function performed in the stage

Two other components that combine with the component to perform its function

 

A

 

 

 

 

 

 

B

 

 

 

 

 

 

C

 

 

 

 

 

 

D

 

 

 

 

 

           
(c)        Draw in Table 2, the circuit symbol of components A, B, C and D.
(d)        State in Table 2, one stage where each where each component can be found in a TV receiver.
(e)        State in Table 2, one function performed by each component in the stages mentioned
in 3 (d).
(f)         List in Table 2, two other components that combine with each of the components to perform the function mentioned in 3 (e).
(g)        Count and record the number of pins on component B.
(h)        State two steps required to remove a faulty component B from a TV receiver.
(i)         Assuming components A, B, C and D are faulty, complete Table 3 with the symptoms of fault in a TV receiver in relation to the associated stages.

 

 

                                                            Table 3


Components

Two symptoms of fault

 

A

(i)

(ii)

 

B

(i)

(ii)

 

C

(i)

(ii)

 

D

(i)

(ii)

 

            (j)         Place component E on a plane surface as shown in Fig. 5.



(k)        Write down the code written on component E.
(l)         Measure and record the resistance of component E.
(m)       State one stage in a TV receiver where component E can be found.
(n)        State one function performed by component E in the stage mentioned in 3 (m).
(m)       State one symptom of faulty component E in a TV receiver.

Observation

 

 The expected responses were:


Table 2

 

(b)

(c)

(d)

(e)

(f)

 

Name of component

Circuit symbol

Stage found in TV receiver

Function performed in the stage

Two other components that combine with the components to perform function

A

RF tuner

LC Oscillator : Circuit, Types, Derivation, and Its Applications

Input stage/RF stage

  • Amplification
  • Channel selection
  • Antenna/LNB
  • RF amplifier
  • Transistor
  • Capacitor

B

Line transformer

Difference between Current Transformer and Potential Transformer |  Electrical Academia

  • Horizontal scanning stage
  • Video output stage
  • Line scanning and synchronizing
  • Generation of high voltage/EHT for the operation of the picture tube
  • Power transistor
  • Capacitor
  • Resistor
  • Integrated circuit

C

Loud speaker

Speakers and DCC - The DCCWiki

Sound/audio output

  • Converts electrical to sound energy
  • Sound reproduction
  • Power transistor
  • Capacitor
  • Resistor

D

Indoor antenna

IEC 60417 - 5039-1973, Aerial (USA: Antenna)

Input/RF stage

  • Radio wave sampling
  • Intercepts radiated RF signal
  • RF tuner
  • Inductor
  • Capacitor

 

                                                                                                                       
(g)        10 pins 

                                                                                                                       

(h)        Steps required to remove a faulty component B from a TV receiver     

  • Discharge the anode cap
  • Heat up the soldering iron to melt the solder
  • Remove the molten solder with lead sucker and pull component out
  • Pull the component out from the board.

 (i)                                                        Table 3


Component

Two symptoms of fault

A

  • No signal reception
  • Poor reception
  • Overlapping of channels

B

  • No raster
  • No horizontal scanning
  • No picture display
  • Picture blinking

C

  • No sound output
  • Poor quality of sound
  • Distorted sound output

D

  • Poor signal reception
  • No signal reception
  • Ghosting/negative picture

 (k)       4W8Ω2K                                                                                                                   
(l)   7.4 Ω - 9.0Ω                                                                                                       
(m)       Power stage                                                                                                    
(n)        Voltage dropping         

 

                                                                                              
(o)        Symptom of faulty component E in TV receiver

  • No power output
  • Poor regulation
  • Low power supply

 

In question 3, candidates were expected to identify unknown circuit components and state their relevance in the various stages of a television receiver. The Chief Examiner reported that the tasks in this question seemed to be very popular among the candidates and majority of the candidates that attempted the tasks responded quite well.