Detecting Interference
DETECTING INTERFERENCECheck the radio in both the AM and FM modes.
A source of interference can only be recognized using the interference audible in the loudspeaker. The following characteristics are typical for individual sources of interference:
1. INTERFERENCE CAUSED BY THE IGNITION SYSTEM
Engine-speed-dependent sizzling and crackling.
To determine this, accelerate the engine while the vehicle is stationary (do not exceed the maximum permissible speed), then switch off the ignition. The interference noise must disappear when the ignition is switched off.
2. INTERFERENCE CAUSED BY THE ALTERNATOR
Engine-speed-dependent whistle. The pitch increases as engine speed increases.
To recognize this interference, remove the V-belt and run the engine briefly. The interference noise must no longer be audible.
3. INTERFERENCE CAUSED BY AUXILIARY UNITS
Windshield wiper motor, radiator fan motor, windshield washer pump, fresh air blower, electric fuel pump, Etc.).
Howling and sizzling interference when the unit is switched on. The interference disappears when the appropriate unit is switched off.
SCOPE OF STANDARD INTERFERENCE-SUPPRESSION WORK - ONLY IN THE CASE OF FACTORY INSTALLED RADIOS
1. Partially shielded spark-plug connectors (5k each).
2. Suppression angle connectors on the ignition leads to the distributor and to the ignition coil (1k each).
3. Suppression distributor rotor (5k), (1k on vehicles with TCI systems).
4. Shielding on the ignition distributor.
5. Interference suppression filter on the ignition distributor in the green lead, terminal 1 (not on vehicles with TCI).
6. Suppression capacitor on the alternator, terminal B+ (2.2 uf).
7. Ground strap between engine hood and body. There may also be additional straps between block and coil or block and radiator mounting.
8. Auxiliary units with full interference suppression such as the windshield wiper motor, (the interference can also be suppressed subsequently using an interference-suppression filter), the radiator cooling fan motor and the fresh air blower.
THE RADIO DOES NOT PLAY AT ALL OR ONLY NOISE IS HEARD
Test conditions:
The antenna is fully extended, (the lower section should never be pushed in to shorten the antenna).
The reception must only be assessed in the open, never inside the workshop (observe the local reception conditions).
Fuse (behind cover above the loudspeaker connections) in radio ok.
During m.y. 1994 amplified roof mounted antennas are installed with the 12 volt supplied through the coaxial antenna cable.
RADIO ONLY RECEIVES A FEW STATIONS
The antenna is completely extended.
NOTE
In the case of vehicles with a roof-mounted antenna, the antenna extension cable is also to be checked. However, remember that the cable, when measured with an ohmmeter, does not indicate continuity because of the built-in capacitor. To make a correct diagnosis, use a test cable of the same type.
The reception must only be assessed in the open, never inside the workshop (observe the local reception conditions).
DISTORTED SOUND ONLY WITH RADIO RECEPTION
Test conditions
The Battery is fully charged.
The vehicle engine is not running.
The reception must only be assessed in the open, never inside the workshop.
SOUND DISTORTED ONLY WHEN PLAYING CASSETTE
Test conditions:
Radio reception is ok on AM and FM modes