1994 MITSUBISHI 3000GT Workshop Manual

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iA-3Mixed with noise, only at night (AM).
L
ii
i
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 changeto a different station or the appearance of a
beating sound* may occur.
Beat sound*: Two signals close in frequency
interfere with each other, creating a repetitious
high-pitched sound. This sound is generated
not only by sound signals but by electrical waves
as well.
2.Factors due to vehicle noise: Generator noisemay be a cause.
the
lamps OFF?
Yes
t1 Do the following measures eliminate the noise? 1 yes cl/l Tune to a station with a strong signal.
l
Tune to a station with a strong signal without com-cletelv extending the antenna.
No
IDoes the noise fade away when the vehicle har-ness is moved away from the radio chassis?
(if the harness is not in the proper position).
NoIf there is more noise than other radios, consult a service
center.
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A-4
Broadcasts can be heard but both AM and FM have a lot of noise.
(1)Noise occurs when the engine is stopped.
YesJ
(2)Noise occurs when the engine in running.
Do the following measures eliminate the noise?
@ Tune to a station with a strong signal.
l Extend the antenna completely. (Whip antenna)
l Adjust the sound quality to suppress high tones.
NoIs the radio body ground mounted securely?
Yes
Securely tighten the nuts for the bodyground.
Yes
YesClean the antenna plug and ground
wire mounting area. Mount the anten-
na securely. On a vehicle with a motor
antenna, check the antenna itself. (Re-fer to E-1, 2.)
If there is more noise than other radios, consult a servicecenter
NOTE
About noise encountered during FM reception only.
Due to differences in FM and AM systems, FM is
noise interference (first fading and multipath). (Refer
to A-2.)
not as susceptible as AM to interference from en-
gines, power lines, lightning, etc. On the other hand,
problem with the radio.>waves of noise or distortion generated by typical
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A-5There is more noise either on AM or on FM.1. There is much noise
onlv on AM
Due to differences in AM and FM systems, AM
is more susceptible to noise interference.Were conditions such as the following present when noise was received?
l Lightning was flashing. A motorcycle was passing.
l
Avehicle passed close by, but it appeared to be avehicle generating a particularlylarge amount of noise radiation.
l Passed beneath a power line. Passed under a bridge.
l Passed beneath a telephone line.
l Passed close by a signal generator.
l Passed close by some other source of electrical noise.
.I-!
I
NO
Yes
. .F- Norse prevenoon on Me radro srde IS difficult. If theproblem is particularly worse than other radios, consulta service center.Continue to check for static; whe
the conditions listed aboveNoYest
If the problem is particularly worse than
other radios, consult a service center.
2. There is much noise only on FM
Due to differences in FM and AM systems, FM
is not as susceptible as AM to interference from
engines, power lines, lightning, etc. On the other
hand, there are cases due to the characteristicsof FM waves of noise or distortion generated
by typical noise interference (first fading and
multipath). (Refer to A-2)
curs in weak signal areas such as mountainous
regions, but this is not due to a problem with
the radio.>
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A-6There is noise when starting the engine.
Noise type
Sounds are in pa-
rentheses ( ).
AM, FM:
Ignition noise
(Popping, Snap-
ping,Cracking,
Buzzing)
Otherelectrical
components
Static electricity
(Cracking, Crin-
kling)
Conditions
0Increasing the engine speedcausing the popping sound tospeed up, and volume de-creases.0Disappears when the ignitionswitch is turned to ACC.
-
lDisappears when the vehicle is
completely stopped.Occurs when parts or wir-
Severe when the clutch is en-ing move for some reasonlgaged.and contact metal parts of
the body.
lVarious noises are produced de-pending on the body part of thevehicle.
Due to detachment from
the body of the front hood,
bumpers, exhaust pipe
and muffler, suspension,
etc.
Causel
Mainly due to the
spark plugs.l Due to the enginenoise.
Noise may appear as
electrical components be-
come older.
Parts to be Location of
inspectedparts
or remedy(next page)
Noise con- 1
denser
Ground
cable2, 3
Repair or replace electricalcomponents.
Return parts or wiring to
their proper position.
Caution
1.Connecting a high tension cable to the noise
filter may destroy the noise filter and shouldnever be done.
2.Check that there is no external noise. Since
failure to do this may result in misdiagnosis
due to inability to identify the noise source,
this operation must be performed.3. Noise prevention should be performed by
suppressing strong sources of noise step
by step.
NOTE
1. Condenser
The condenser does not pass D.C. current, butas the number of waves increases when it
passes A.C. current, impedance (resistanceagainst A.C.) decreases, and current flow is
facilitated. A noise suppressing condenser
which takes advantage of this property is in-
serted between the power line for the noise
source and the ground. This suppresses noiseby grounding the noise component (A.C. or
pulse signal) to the body of the vehicle.
2. Coil
The coil passes D.C. current, but impedance
rises as the number of waves increases relativeto the A.C. current. A noise suppressing coil
which takes advantage of this property is in-
serted into the power line for the noise source,
and works by preventing the noise componentfrom flowing or radiating out of the line.
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Ground parts by bonding.
Cases where the problem
is not eliminated by a single
response to one area are
common, due to several
bodypartsbeing
imperfectly grounded.

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NOISE SUPPRESSION PARTS MOUNTING POSITIONS
1/ Noise con::;;, 1
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IA-7Some noise appears when there is vibration or shocks during traveling.
‘d ~
Are connectors properly connected?
YesNo
---+ Ensure proper connection
t
Does noise appear when the radio switch is turned on while theNovehicle is stopped and the radio is struck while tuned away fromLa station?
YesStatic electricity noise:
Body static electric from the shock absorber rubber bushings used
to prevent vibration, tires, etc. occurs because of separation fromthe ground, causing a buzzing noise.
Since no measures can be taken on the radio side, steps shouldbe taken to discharge the static electricitv of the vehicle bodv.
tIs the radio correctly grounded?
(Is the mounting screw tightened securely?)
1 Yes
tIs the antenna correctly grounded? (If noise appears when the Nocantenna is moved, this means the ground is not securely con-
nected.)
If rust is present on the antenna ground screw, clean and tightenthe ground securely.
Yes
1 Reoair or reolace radio.1
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A-8Noise sometimes appears on FM during traveling.
NoIs the antenna completely extended?
Yes
t Check the antenna itself.
(Refer to E-l, 2.)
+Does the problem clear up whenre
1 No
Yes
iDoes the problem appear only in certain locations and only with yes
certain stations?
No
~ Due to electrical field conditions. (Multipath
noise*, fading noise*).
Are connectors property connected?
Yes
Check connector connections.1
tDoes noise appear when the radio switch is turned on while the
vehicle is stopped
and the radio is struck while tuned away froma station?
Yes
No*Static electricity noise:Sody static electric from the shock absorberrubber bushings used to prevent vibration, tires,etc. occurs because of separation from the
ground, causing a buzzing noise.
Since no measures can be taken on the radioside, steps should be taken to discharge the
static
electricitv of the vehicle bodv.
Is the radio body correctly grounded?
No(Is the mounting screw tightened securely?
)
Yes
-) Tighten the screw securely.I
Is the antenna correctly grounded? (If noise appears when the antennais moved, this means the ground is not securely connected.)
Yes
If rust is present on the antenna ground screw,clean and tighten the ground securely.
*
1 Repair or replace radio.1
About multipath noise and fading noise
Because the frequency of FM waves is extreme-
ly high, it is highly susceptible to effects from
geological formations and buildings. These ef-
fects disrupt the broadcast signal and obstruct
‘reception in several ways.l Multipath noise
This describes the echo that occurs when the
broadcast signal is reflected by a large obstruc-
tion and enters the receiver with a slight time
delay relative to the direct signal (repetitious
buzzing).l Fading noise
This is a buzzing noise that occurs when the
broadcast beam is disrupted by obstructing ob-
jects and the signal strength fluctuates intricately
within a narrow range.
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IA-9Ever-present noise.I
Noise is often created by the following factors, and
often the radio is OK when it is checked individually.l Traveling conditions of the vehicle
l Terrain of area traveled through
l Surrounding buildings
l Signal conditions
l Time periodFor this reason, if there are still problems with noiseeven after the measures described in steps A-l
to A-8 have been taken, get information on the fac-
tors listed above as well as determining whetherthe problem occurs with AM or FM, the station
names, frequencies, etc., and contact a service cen-
ter.B. RADIO
IB-lNo power is supplied when the switch is set to ON.IIIIs multi-purpose fuse No. 4 blown or is the circuit open?Replace fuse or repair harness.
NoIs the connector at the back of the radio connected properly?
Yes
Connect connector securely.1t
NoDisconnect and check the connector at the rear of the radio. Is the ACC / Repair harness.
power (12 V) being supplied to the radio?J
I
Yes
1 Reoair or reolace radio.
1 B-2No sound from one speaker.ICheck to see if there is any sound when attached
to another radio.
I-=----[Repair or replace radio unit.
No
checkthespeakerharnessfor conductance.
out.*Speakarj
NoRepair speaker harness and ensure
proper connection of relay connectors.
tRepair or replace speaker.
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