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)
A	(ii)
B	(i)
B	(ii)
C	(i)
C	(ii)
D	(i)
D	(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		Input stage/RF stage	Amplification Channel selection	Antenna/LNB RF amplifier Transistor Capacitor
B	Line transformer		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		Sound/audio output	Converts electrical to sound energy Sound reproduction	Power transistor Capacitor Resistor
D	Indoor 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.