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3V-8
RADIO SOUND SYSTEMS
S M A L L CLIP
C A P A C I T O R
A J 4 2 2 4 9
Fig. 3V-13
Interference Eliminator Test Device
In general, any adjacent metal parts which are sepa-
rated by mastic or paint must be connected together
electrically.
Effective bonding requires more than physically clean
surfaces and self-tapping screws. Tooth-type lockwa-
shers must be used to cut into the surface layers of
metal. Grounding straps must be as short and as heavy
as possible.
A-line noise is normally the result of:
• Alternator whine (A-line)
• Wiring harness too close to ignition wiring
• Radio noise suppressor
• Poor radio grounding
Alternator Whine (A-Line)
Alternator whine does not stop instantly when the key
is turned quickly to the accessory position at fast idle. It
is a high pitched whine which increases with rpm. Cor-
rect alternator whine as follows:
(1) Install a 0.5 to 2.0 mfd bypass capacitor from the
alternator output terminal to ground (fig. 3V-14).
Fig. 3V-14 Alternator Noise Suppression
(2) Install a coaxial capacitor in alternator output
wire (fig. 3V-14).
(3) Replace alternator diodes.
Wiring Harness Close to Ignition Wiring
Noise carried to the radio normally can be corrected as
follows:
(1) Relocate harness wiring away from ignition
wires.
(2) Install 0.5-mfd capacitors on each fuse panel
lead. Be sure capacitor is grounded.
Instrument Cluster Radio Noise Suppressor
A noise suppressor is installed on Cherokee, Wagon-
eer and Truck models equipped with a radio. This sup-
pressor (choke) is plugged into the back of the cluster on
a printed circuit board. Be sure the choke has not been
installed over the copper strip installed on vehicles not
originally equipped with a radio.
Tap on the instrument panel with the ignition in the
On position and the Acc position to activate the CVR
point movement. If noise only occurs in the On position,
repair noise suppressor as follows:
(1) Remove radio choke.
(2) Remove plastic covering.
(3) Unsolder one end of coil wire and remove ap-
proxiately 6-1/2 inches of wire.
(4) Resolder wire end.
(5) Wrap coil with several turns of plastic electrical
tape and install choke.
Poor Radio Ground
To check for a poor ground, attach a jumper wire to
the radio case and connect to a good chassis ground. If
there is no change in radio noise, the radio has a good
ground.
If noise changed, check for loose mounting screws and
a poor ground.
Othsr Sources of Interference
Speaker Leads
To determine if speaker leads are inducing or picking
up noise, lay the wires on top of the carpet with the
wires separated. If the noise is gone, the harness is at
fault. Perform one or more of the following:
(1) Separate coil wires by installing a loom over
each of the wires.
(2) Install a 0.001-mfd, thumbnail-type capacitor
across each speaker.
(3) Remove ground wire from harness and ground
each rear speaker at the rear of vehicle.
Speaker-induced noise will normally not occur on
front-mounted instrument panel speaker systems. It is
more apt to occur on four-speaker systems and when the
fader control is in the mid-position.
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M F D
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Troubleshooting
