Radio,Television And Electronic Paper 3, WASSCE (SC), 2017

Question 2

 

  • AIM: To test the candidates’ knowledge on different sections of colour CRT Television receiver.

    1. You are provided with a colour CRT Television receiver.
    2.   Let the Supervisor open the back cover of the Television receiver.
    3.   List two tools used by the Supervisor in removing the back cover of the Television.
    4. State the specification of the Television in terms of:
    5. model;
    6. input supply voltage;
    7. supply frequency;
    8. input power rating.
    9. Identify one transducer in the audio section and record in Table 2.
    10. Write in Table 2, the function of the transducer identified in (e).
    11. State two physical features of the transducer and record in Table 2.
    12. Identify two components found in the audio section and record in Table 2.
    13. Repeat steps (e) to (h) for the video section
    14. List two faults associated with the section specified in Table 2.

    Table 2


    Section

    Transducer

    Function of transducer

    Physical feature of transducer

    Components identified

    Fault associated with section

    Video section

     

     

     

     

     

     

     

    Audio section

     

     

     

     

     

     

     

    1. State two precautions taken in carrying out the activities.
  • Observation

    The expected answers were:

    (c) Tools used to remove the backcover of television

    • Screw drivers
    • Allen key
    • A pair of pliers/long nose pliers        

                                                                  
    (d) (i) Model

    • 21SB1RG-TB
    • KV-LS21T99
    • Any other  acceptable model                                                                        

          (ii) Input supply voltage        -       110 – 240V                                                                                              
    (iii) Supply frequency           -         50/60Hz                                                        
    (iv) Power rating                   -        40W – 85W (varies with model) 

    Table 2


    Section

    Transducer

    Function of transducer

    Physical feature of transducer

    Components identified

    Fault associated with section

    Video Section

    Cathode Ray Tube (CRT)

     

     

     

     

    Converts electrical energy to video/picture/light

     

     

     

       

    -HT input cap
    -connecting pins
    -screen
    -phosphor screen glass envelop
    -hollow shape

     

    -Inductor/coil
    -resistor
    -capacitor
    -transistor
    -HT/line transformer
    -I.C.
    -RBG board
    -diode
    -matrix

    -no picture
    -blurred picture
    -dancing/rolling picture
    -elongated picture
    -reduced picture
    -loss of video signal

    Audio Section

    Speaker

     

     

     

    Converts electrical energy to sound

     

     

       

    -magnet
    -diaphragm
    -coil
    -cast/metal frame
    -conical shape

     

    -resistor
    -capacitor
    -diode
    -I.C.
    -LED
    -transformer
    -transistor
    -inductor

    -no sound
    -humming sound
    -hissing sound
    -loss of volume

     

     

    (k) Precautions in carrying out the activities

    • I ensured the use of the right tools for the right jobs.
    • I disconnected television set from power source before opening.
    • I discharged the anode cap of the H.T. transformer.
    • I discharged the high voltage capacitors.
    • I wore protective dressing.
    • I used insulated tools.
    • I grounded/earthed the high voltage sections.

    Candidates were expected to read off the specification of the Television receiver at on back cover. Basically, only the Cathode Ray Tube and the loudspeaker can convert from one form of energy to the in the video and audio sections respectively. Therefore, candidates were expected to identify them as transducers.