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Interference noises due to all loudspeakers

NOTE: The loudspeaker leads are twisted together as standard.
RADIO SYSTEM DIAGNOSIS FOR INTERFERENCE NOISES DUE TO ALL LOUDSPEAKERS

Work instruction Yes No
1 Check all connections to the amplifier or the radio. Take particular note of loose or bent pins, corrosion or other damage.
Damage present?		 Repair the lead connection.
Noise still present? Step 2.
Noise remedied? End		 Step 2
2
  1. Localise the ground connection cable of the amplifier.
  2. Disconnect the ground connection cable on the amplifier side.
  3. Lay the ground connection cable separately and connect.
  4. Check the ground connection with an ohmmeter at the negative terminal of the battery.
Noise still present?		 Disconnect all amplifiers but one from the power supply. Step 3 End
3
  1. Check all connections of the amplifier.
  2. As an experiment, insert a functional amplifier in place of the suspected defective one.
Noise still present?		 Step 4 Replace amplifier End
4 Disconnect the audio inputs from the amplifier, whereby the connections B+ and ground must be maintained. Noise still present? Step 5 Repair the audio connecting cable, lay it again or replace. End
5 If the amplifier is switched on via a relay, remove the relay and connect the amplifier directly to the power supply.
Noise still present?
  1. Localise the battery connecting cable of the amplifier.
  2. Cut this cable.
  3. Install an interference filter at the cut point.
End		 Replace the closing relay of the amplifier. End
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