Radio,Television And Electronic Paper 2, WASSCE (SC), 2018

Question 1

  1. State three:

(i)         parts of a Cathode Ray Tube (CRT) television receiver that can cause electric shock;
(ii)        safety precautions in handling the CRT of a television receiver.

          

  1. Table 1 shows some symptom of faults in a CRT television receiver.

Table 1          

 

Symptoms

Two faulty stages/sections

1.

No raster, no picture but sound normal

 

 

2.

Raster and picture normal but no sound

 

 

3.

Raster normal but no picture and no sound

 

 

Complete Table 1 by stating two stages/sections to which each symptom of fault is associated.


Observation

The expected answers were:
   (a)        (i)        Parts of a Cathode Ray Tube (CRT) television receiver that can cause electric shock

  • Anode cap and connector of flyback transformer
  • High voltage cable/power cord
  • Yoke assembly
  • Flyback transformer
  • High voltage capacitors/filter capacitors
  • Heat sink
  • CRT chassis/degaussing coil

             (ii)      Safety precautions in handling the CRT of a television receiver

  • Turn off the power and disconnect the a.c. power cord before removing the back cover of the receiver.
  • Remove any metal jewelry on your body and work area.
  • Do not work in isolation. Always have someone nearby in case of an accident/emergency.
  • Wear appropriate personal protective/safety devices.
  • Avoid holding the tube by the neck.
  • Discharge high voltage capacitors.
  • Avoid water spillage on the floor and work area.
  • Avoid overcrowding the work area with tools.

(b)                                                       Table 1

 

Symptoms

Two faulty stages/sections

1.

No raster, no picture but sound normal

EHT circuit

Scanning coil

Vertical output

Line output stage

Picture tube

Biasing of picture tube

Socket connections

Video output circuit

2.

Raster and picture normal but no sound

Sound/audio section

Sound I.C./power transistor/audio amplifier

Loudspeaker

3.

Raster normal but no picture and no sound

Antenna

Feeder line

RF tuner circuit

Video section

IF amplifier

Video detector

AGC

Sync separator

Only a few candidates attempted question one and the responses of these candidates were reported to be poor. Safety precautions in handling a CRT television receiver, faults and troubleshooting should be well taught by teachers as this is an important aspect of the subject.