Mitsubishi Colt Ralliart. Manual — part 489

RADIO AND CD PLAYER

CHASSIS ELECTRICAL

54A-101

INSPECTION PROCEDURE 4: Noise is Present while Moving (FM).

ACX01869

10kW
output FM
broad cast

For stereo:
20 - 25 km

For monaural:
30 - 40 km

For home stereos:
80 - 90 km

Multipath interference

First fading
interference

AC

DIAGNOSIS PROCEDURE

NOTE: FM waves have the same properties as lamp,
and can be deflected and blocked. FM signal recep-
tion is severely degraded in the shadow of obstruc-
tions such as buildings or mountains. An FM receiver
will then only receive a reflected signal.
1. The signal becomes weak as the distance from

the station's transmission antenna increases. The
signal strength received depends on the signal
strength of the transmitting station and intervening
obstructions such as buildings and hills. Generally
speaking, the area of good reception is
approximately 20

− 25 km for stereo reception,

and 30

− 40 km for monaural reception.

2. The signal will becomes weak when an area of

shadow from the transmitting antenna (places
where there are obstructions such as mountains
or buildings between the station transmitter and
the vehicle), and noise will appear. <This is called
first fading, and gives a steady buzzing noise.>

3. If a direct signal hits the antenna at the same time

as a signal reflected by obstructions such as
mountains or buildings, interference of the two
signals will generate noise. When moving, noise
will appear each time the vehicle's antenna
passes through this kind of obstructed area. The
strength and interval of the noise varies according
to the signal strength and the conditions of
deflection. <This is called multipath noise, and is a
repetitive buzzing.>

4. Since FM stereo transmission and reception has a

weaker field than monaural, it is often
accompanied by a hissing noise.

After taking measures to prevent the noise, check
that no noise occurs.
5. Change to a different station with a stronger wave

to boost resistance to interference.

6. Suppress high tones to reduce noise.
7. Extend antenna completely.
If there is noise, the following causes can be consid-
ered.
8. If due to vehicle noise: It may not be possible to

prevent noise if the signal is weak.

9. If due to external noise: In almost all cases,

prevention on the receiver side is not possible.
Weak signals especially are susceptible to
interference.

If there is more noise than on radios in other vehi-
cles, find out the noise condition and the name and
frequency of the receiving stations from the owner,
and consult with the radio manufacturer's service
centre.

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RADIO AND CD PLAYER

CHASSIS ELECTRICAL

54A-102

INSPECTION PROCEDURE 5: Mixed with Noise, Only at Night (AM).

The following factors can be considered as possible
causes of noise appearing at night.
1. Factors due to signal conditions: Due to the fact

that long-distance signals are more easily
received at night, even stations that are received
without problem during the day may experience
interference in a general worsening of reception
conditions. The weaker a station is the more
susceptible it is to interference, and a change to
different station or the appearance of a beating
sound* may occur.
NOTE: Beat sound*: Two signals close in fre-
quency interfere with each other, creating a repeti-
tious high-pitched sound. This sound is generated
not only by sound signals but electrical waves as
well.

2. Factors due to vehicles noise: Alternator noise

may be a cause.

DIAGNOSIS PROCEDURE

Step 1. Check that the noise still obvious even
when the lamps are off.

Q: Is the noise still obvious even when the lamps are

off?
YES :

Go to Step 2.

NO :

Go to Step 3.

Step 2. Check hat the following actions.
(1) Tune to a station with a stronger wave.
(2) Tune to a station with a stronger wave without

completely extending the antenna (Mast
antenna).

Q: Is there more noise than on radio in other

vehicles?
YES :

Consult the radio manufacturer's service

centre.

NO :

Check that there is no noise.

Step 3. Check that the noise fades away when the
vehicle harness is moved away from the radio (if
the harness is not in the proper position).

Q: Does the noise fade away when the vehicle

harness is moved any from the radio (If the
harness is not in the proper position)?
YES :

Consult the radio manufacturer's service

centre.

NO :

If there is more noise than other radios,
consult the radio manufacturer's service
centre.

INSPECTION PROCEDURE 6: Broadcasts can be Heard but Both AM and FM have a lot of Noise.

DIAGNOSIS PROCEDURE

Step 1. Check the state of the antenna.

Q: Is the mast antenna assembled?

YES :

Go to Step 2.

NO :

Assemble the mast antenna. Check to see
that the noise is gone.

Step 2. Check that the noise occur when the
engine is stopped or the engine is running.

Q: Does noise occur when the engine is stopped or

the engine is running?
When the engine is stopped :

Go to Step 3.

When the engine is running :

Check the vehicle's

noise suppressor (Refer to Inspection
Procedure 9

P.54A-105

).

Step 3. Check that the following actions
disappear the noise.
(1) Tune to a station with a stronger wave.
(2) Extend the antenna completely (Mast antenna).
(3) Adjust the sound quality to suppress high tones.

Q: Is the noise eliminated?

YES :

Consult the radio manufacturer's service

centre.

NO :

Go to Step 4.

Step 4. Check that the radio is correctly earthed
The radio is connected to the earth with an assem-
bling screw.

Q: Is the radio correctly earthed?

YES :

Go to Step 5.

NO :

Consult the radio manufacturer's service
centre.

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RADIO AND CD PLAYER

CHASSIS ELECTRICAL

54A-103

Step 5. Check the connection of the antenna plug
and radio and CD player.

Q: Is the antenna plug thoroughly connected to the

radio and CD player?
YES :

Go to Step 7.

NO :

Go to Step 6.

Step 6. Check that the noise is eliminated when
the antenna plug is properly attached.

Q: Is the noise eliminated?

YES :

Consult the radio manufacturer's service

centre.

NO :

Go to Step 7.

Step 7. Check that the antenna is in good
condition and is it properly mounted.

Q: Is the antenna in good condition and is it properly

mounted?
YES :

Consult the radio manufacturer's service

centre.

NO :

Either repair or replace the antenna
assembly. Check to see that the noise is
gone.

INSPECTION PROCEDURE 7: There is More Noise on Either AM or FM.

DIAGNOSIS PROCEDURE

There is much noise only on AM. Due to differences
in AM and FM systems, AM is more susceptible to
noise interference.

Step 1. Check that there is noise under the
following state(s).

• A motorcycle was passing.

• Lighting was flashing.

• A vehicle passed close by, but it appeared to be a

vehicle generating a particularly large amount of
noise radiation.

• Passed beneath a power line.

• Passed beneath a telephone line.

• Passed close by a signal alternator.

• Passed close by some other sources of electrical

noise.

• Passed under a bridge.

Q: Is there noise in the above states?

YES :

Go to Step 3.

NO :

Go to Step 2.

Step 2. Continue to check for static; when static
is detected, check for the conditions listed
above.

Q: Is there noise in the state described in Step 1?

YES :

Noise prevention on the radio side is

difficult. If the problem is particularly worse
than other radios, consult a service centre.

NO :

Go to Step 3.

Step 3. Check noise prevention on the radio side
is difficult.

Q: Is the noise level worse than other radios?

YES :

Consult a service centre. Noise

encountered during FM reception only. Due
to differences in FM and AM systems, FM is
not as susceptible as AM to interference
from engines, power lines, lighting, etc. On
the other hand, due to the characteristics of
FM waves, there are sometimes cases of
noise or distortion which are generated by
typical noise interference (first fading and
multipath). <Noise (hissing) occurs in weak
signal areas such as mountainous regions,
but this is not due to Furthermore, the
amount of interference will be comparatively
less for vehicles equipped with a diversity
antenna system*. If there is an equivalent
amount of distortion in vehicles or radios of
the same type, then differences will be
because of differences in antenna systems,
and this should be explained to the user. a
problem with the radio.> Furthermore, the
amount of interference will be comparatively
less for vehicles equipped with a diversity
antenna system*. If there is an equivalent
amount of distortion in vehicles or radios of
the same type, then differences will be
because of differences in antenna systems,
and this should be explained to the user.

NO :

f the noise level is roughly the same as
other radios, there is no action to be taken.

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RADIO AND CD PLAYER

CHASSIS ELECTRICAL

54A-104

INSPECTION PROCEDURE 8: There is Noise when Starting the Engine.

DIAGNOSIS PROCEDURE

CAUTION

• Connecting a high tension cable to the noise

filter may destroy the noise filter and should
never be done.

• Check that there is no external noise. Since

failure to do this may result in an incorrect
diagnosis due to the inability to identify the
noise source, this operation must be per-
formed.

• Noise prevention should be performed by

suppressing strong sources of noise step by
step.

NOTE: Capacitor: The capacitor does not pass DC
current, but as the number of waves increases when
it passes AC current, impedance (resistance against
AC) decreases, and current flow is facilitated. A
noise suppressing capacitor which take advantage of
this property is inserted between the power line for
the noise source and the earth. This suppresses
noise by earthing the noise component (AC or pulse
signal) to the body of the vehicle.

NOTE: Coil: The coil passes DC current, but imped-
ance rises as the number of waves increases relative
to the AC current. A noise suppressing coil which
takes advantage of this property is inserted into the
power line for the noise source, and works by pre-
venting the noise component from flowing or radiat-
ing out of the line.

Noise type sounds are in
parentheses

Conditions

Cause

Remedy

AM or FM: ignition noise
(popping, snapping,
cracking, buzzing)

• Increasing the engine

speed causes the
alternator whine
sound to speed up
and the volume to
decrease

• Disappears when the

ignition switch turned
to "ACC."

• Mainly due to the

spark plugs

• Due to engine noise

• Check or replace the

earth cable.

• Check or replace the

noise capacitor.

Other electrical
components

−

Noise may occur as the
electrical components
become older.

Repair or replace the
electrical components.

Static electricity (cracking,
crinkling)

• Disappears when the

vehicle is completely
stopped.

• Severe when the

clutch is engaged

Occurs when parts or
wiring move for some
reason and contact metal
parts of the body.

Return parts or wiring to
their proper position.

Static electricity (cracking,
crinkling)

• Various noise are

produced depending
on the body part of the
vehicle.

Due to removal of the
front hood, bumpers,
exhaust pipe and muffler,
suspension, etc.

Earth parts by bonding.
Cases where the
problem is not eliminated
by a signal response to
one area are common,
due to several body parts
being imperfectly
earthed.

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