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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