Introduction to Dead Fault
1. Dead Fault
a) Clean the battery contacts and test the battery.
b) If battery eliminator is employed, test its output dc voltage. If output voltage is acquired.
c) Test power cord, power transformer diodes, on-off switch, and capacitor. Also solder the output leads correctly. If the receiver is still dead even after the output of battery eliminator is acquired.
d) Test the speaker and coupling capacitor of speaker.
e) Test the output transistors and their biasing resistors.
f) Test the driver transformer, voltage amplifier transistor and their biasing resistors.
g) I.F transistors, mixer transistor and decoupling capacitors might get short circuited.
h) Dry soldering might be happened.
i) Copper print might be opened.
2) 'HUM' IN RECEIVER
a) If pulsating dc is supplied (in its place of pure dc) to a receiver, a 'hum' sound is heard.
b) Defective filter capacitors
c) Also test power transformer and diodes
a) Shorted output Transistors
b) Shorted driver transformers and voltage amplifier transistors.
c) IF Transistors, Shorted filter Capacitors, Mixer Transistor and decoupling Capacitors.
4) LOW VOLUME
a) From eliminator Low output voltage
b) Leaky output Transistors (AC128 x 2)
c) Defective speaker and speaker coupling capacitor
d) IFTs might be mis aligned; broken cores
e) Defective volume control
f) Defective OA 79 detector diode
5) Just HISS SOUND IS HEARD IN THE RECEIVER; NO RECEPTION OF RADIO STATIONS (NO SIGNAL)
a. Defective oscillator coil
b. Check mixer transistor BF 194B and its biasing voltage
c. Defective Ganged capacitor
d. Shorted trimmer
e. Band switch open
f. Dry soldering; copper print open
6) ONLY FEW RADIO STATIONS IS RECEIVED
a) Mis aligned antenna coil
b) Check mixer transistor
c) Defective Gang
d) IFTs should not be aligned properly
e) Dry soldering; Copper print cut
7) NOISY RECEPTION
a) Misaligned antenna coil
b) IFTs misaligned
c) Chassis earth is improper
d) Trimmer should be aligned correctly
e) Loose connection in AC power card.
8) RECEPTION WITH WHISTLING SOUND
a) Defective oscillator coil
b) Defective Gang, Trimmer
c) First IFT and Oscillator coil should be aligned suitably
9) DISTORTED AUDIO
a) Check the output Transistors, Speaker and its coupling capacitor.
b) Misaligned IFTs
c) Mismatching of audio o/p transistors
10) INTERMITTENT RECEPTION
Dry soldering (or) copper print cut. First rectify it and then the PCB should be undergone vibration test. If the defect still persists
a) Defective speaker
b) Defective volume control, on-off switch
c) Improper position of batteries
d) Improper connections of eliminator
e) After rectifying this fault, the receiver should be Soak tested.
11) MOTOR BOATING SOUND FROM RECEIVER
While a 'dub', 'dub' sound is heard from radio receiver, this type of defect is termed as motor boating.
a) test the B+ capacitor and decoupling capacitors
12) A RECEIVER IS WORKING IN LOW FREQUENCYAND BUT NOT IN HIGH FREQUENCY END
13) NOISE PRODUCED WHILE TUNNING
14) NOISE HEARD WHILE VOLUME CONTROL IS VARIED
Defective volume control. It have to be cleaned with kerosene.
15) RADIO STATIONS RECEIVED IN WRONG LOCATIONS IS THE DIAL
Improper alignment of oscillator coil and its trimmer.
16) FULL VOLUME; VOLUME CANNOT BE REDUCED
Defective volume control or its earth may be disconnected.
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