Lexus RX300 (MCU15). Service manual - part 150

BE1YN–01

I04188

Wire Harness Side

I08150

Connector ”B”

Connector ”C”

Connector ”A”

Wire Harness Side

–

BODY ELECTRICAL

AUDIO SYSTEM (Europe)

BE–147

LEXUS RX300   (RM785E)

INSPECTION

1.

INSPECT CD AUTO CHANGER CIRCUIT

Disconnect connectors from CD auto changer and inspect the
connector on the wire harness side.

Tester connection

Condition

Specified condition

8 – Ground

Constant

Continuity

12 – Ground

Ignition switch LOCK

No voltage

12 – Ground

Ignition switch ACC or ON

Battery positive voltage

5 – Ground

Constant

Battery positive voltage

If the circuit is not as specified, inspect the circuits connected
to other parts.
HINT:

S

 Check the wire harness between the radio receiver as-
sembly and the CD auto changer.

S

 Since the signals to and from the MUTE, R

–

, R

+

, L

–

, L

+

,

TX

–

 and TX

+

 terminals are serial signals, they cannot or-

dinarily be measured with a tester.

2.

INSPECT POWER AMPLIFIER CIRCUIT

Disconnect the connector from power amplifier and inspect the
connector on the wire harness side.

I07332

Connector ”B”

Connector ”C”

Connector ”A”

Wire Harness Side

BE–148

–

BODY ELECTRICAL

AUDIO SYSTEM (Europe)

LEXUS RX300   (RM785E)

Tester connection

Condition

Specified condition

A6 – Ground

Constant

Continuity

A3 – Ground

Ignition switch LOCK and radio switch ON

No voltage

A3 – Ground

Ignition switch ACC or ON and radio switch ON

Battery positive voltage

A4 – Ground

Constant

Battery positive voltage

If the circuit is not as specified, inspect the circuits connected
to other parts.

3.

INSPECT RADIO RECEIVER ASSEMBLY CIRCUIT

Disconnect the connectors from the radio receiver assembly,
and inspect the connector on the wire harness side.

Tester connection

Condition

Specified condition

A2 – Ground

Constant

Continuity

A4 – Ground

Constant

Battery positive voltage

A1 – Ground

Ignition switch LOCK

No voltage

A1 – Ground

Ignition switch ACC or ON

Battery positive voltage

HINT:
Check the wire harness between radio receiver assembly and
the CD auto changer, between radio receiver assembly and
power amplifier.

BE1YO–01

30 kHz

300 kHz

3 MHz

30 MHz

300 MHz

LF

MF

HF

VHF

AM

FM

Frequency modulation

Frequency

Designation

Radio wave

Modulation

Amplitube modulation

BE2818

FM (Stereo)

FM (Monaural)

AM

BE2819

Fading

lonosphere

–

BODY ELECTRICAL

AUDIO SYSTEM (Except Europe)

BE–149

LEXUS RX300   (RM785E)

AUDIO SYSTEM (Except Europe)

DESCRIPTION

1.

RADIO WAVE BAND

The radio wave bands used in radio broadcasting are as follows:

LF: Low Frequency
MF: Medium Frequency
HF: High Frequency
VHF: Very High Frequency

2.

SERVICE AREA

There are great differences in the size of the service area for AM
and FM monaural. Sometimes FM stereo broadcasts cannot be
received even through AM can be received in very clearly.
Not only does FM stereo have the smallest service area, but it
also picks up static and other types of interference (”noise”)
easily.

3.

RECEPTION PROBLEMS

Besides the problem of static, there are also the problems
called ”fading”, ”multipath” and ”fade out”. These problems are
caused not by electrical noise but by the nature of the radio
waves themselves.

S

Fading
Besides electrical interference, AM broadcasts are
also susceptible to other types of interference, es-
pecially at night. This is because AM radio waves
bounce off the ionosphere at night. These radio
waves then interfere with the signals from the same
transmitter that reach the vehicle’s antenna directly.
This type of interference is called ”fading”.

BE2820

Multipath

BE2821

Fade Out

AM

FM

Noise occurs at a specific place.

Strong possibility of foreign noise.

Noise occurs when listening to
faint broadcasting.

Noise occurs only at night.

Noise occurs while driving and
at a specific place.

There is a case that the same program is broadcasted
from each local station and that may be the case you are
listening different station if the program is the same.

Strong possibility of the beat from a distant broadcasting.

Strong possibility of multipath noise and fading noise
caused by the changes of FM waves.

BE–150

–

BODY ELECTRICAL

AUDIO SYSTEM (Except Europe)

LEXUS RX300   (RM785E)

S

Multipath
One type of interference caused by the bounce of
radio waves off of obstructions is called ”multipath”.
Multipath occurs when a signal from the broadcast
transmitter antenna bounces off buildings and
mountains and interferes with the signal that is re-
ceived directly.

S

Fade Out
Because FM radio waves are of higher frequencies
than AM radio waves, they bounce off buildings,
mountains, and other obstructions. For this reason,
FM signals often seem to gradually disappear or
fade away as the vehicle goes behind a building or
other obstruction. This is called ”fade out”.

4.

NOISE PROBLEMS

(a)

Questionnaire for noise:
It is very important for noise troubleshooting to have good
understanding of the claims from the customers, so make
the best use of following questionnaire and diagnose the
problem accurately.

HINT:
In the case that the noise occurrence condition does not meet
any of the above questionnaire, check based on the ”Reception
problems”.
Refer to above descriptions for multipath and fading.