Question 3.
- While troubleshooting a malfunctioning radio receiver, a technician discovered that an electrolytic capacitor in the power stage of the receiver is faulty.
State:
- One possible symptom of the fault that would be shown by the radio receiver;
- One method that could be used to discharge the capacitor;
- Two tools that would be required to remove the capacitor from the circuit board;
- Two tools that would be required to replace the capacitor with a functioning one into the circuit board;
- Two precautions that should be observed while replacing the capacitor.
- In the process of troubleshooting the radio receiver in 3(a), the technician consulted its service information manual. State two importance of the manual in the repair of the radio receiver.
(c) List two fault-finding equipment used on radio receivers.
Observation
It was reported that majority of the candidates that attempted Question 3 responded very well. Only a few candidates could not give the required responses..
The expected responses were:
(a) (i) Symptoms that would be shown by the radio receiver
- Humming sound
- Distortion
- Dead set
- Methods of discharging capacitor
- Touching the meter probes
- Using an un-insulated metal
- Tools required to remove capacitor from the circuit board
- Solder wick
- Desoldering pump | lead sucker
- Heat gun | hot air gun
- Removal alloy
- Removal flux
- Heated soldering tweezers
- Long nose pliers
- Tools required to replace the capacitor on the circuit board
- Soldering iron
- Safety glasses
- Soldering stand
- Soldering gun
- Soldering lead | solder
- Wet sponge
- Precautions that should be observed while replacing the capacitor
- Replace with exact value of capacitor
- Avoid contact with the bit | tip | element of the soldering iron
- Avoid contact of the soldering iron with the lead | body of component
- Avoid excessive heat
- Avoid excessive solder
- Ensure the correct polarity of the capacitor
- Avoid dry joints
(b) Importance of the manual in the repair of radio receiver
- It reveals the circuit diagram and path
- It gives the correct specification of component to be replaced
- It gives the values of expected quantities at different points
- It gives the expected waveform at different points
- It helps in identifying faults
(c) Fault finding equipment used on radio receivers
- Logic probe
- Oscilloscope
- Multimeter
- Frequency counter
- Signal tracer