Section 267 (Audio System): Description

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

Fig 1: Radio Wave Bands Graph

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LF: Low Frequency

MF: Medium Frequency

HF: High Frequency

VHF: Very High Frequency

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.

Fig 2: Identifying Service Area

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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.

Fig 3: Identifying Fading

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• Fading

  Besides electrical interference, AM broadcasts are also susceptible to other types of interference, especially 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".

• 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 received directly.

  Fig 4: Identifying Multipath

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• 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".

  Fig 5: Identifying Fade Out Signal

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1. Raise the cassette door with your finger.

   Next, using a pencil or similar object, push in the guide.

2. Using a cleaning pen or cotton applicator soaked in cleaner, clean the head surface, pinch rollers and capstans.
   Fig 6: Identifying Pinch Rollers

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If the disc gets dirty, clean the disc by wiping the surface from the center to outside in the radial directions with a soft cloth.

Fig 7: Identifying Disc

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1. What is AVC-LAN?

   AVC-LAN is the abbreviation, which stands for Audio Visual Communication-Local Area Network. This is a unified standard co-developed by 6 audio manufactures associated with Toyota Motor Corporation.

   The Unified standard covers signals, such as audio signal, visual signal, signal for switch indication and communication signal.

   Fig 8: Identifying Outline Of AVC-Lan

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2. Objectives

   Recently the car audio system has been rapidly developed and functions have been changed drastically. The conventional system has been switched to the multi-media type such as a navigation system. At the same time the level of customers needs to audio system has been upgraded. This lies behind this standardization.

   The concrete objectives are explained below.

   1. When products by different manufactures were combined together, there used to be a case that malfunction occurred such as sound did not come out. This problem has been resolved by standardization of signals.
   2. Various types of after market products have been able to add or replace freely.
   3. Because of the above (2), each manufacture has become able to concentrate on developing products in their strongest field. This has enabled many types of products provided inexpensively.
   4. Conventionally, a new product developed by a manufacture could not be used due to a lack of compatibility with other manufactures products. Because of this new standard, users can enjoy compatible products provided for them timely.

   The above descriptions are the objectives to introduce AVC-LAN. By this standardization, development of new products will no longer cause systematic errors. Thus, this is very effective standard for a product in the future.

   HINT:

   • When +B short or GND short is detected in AVC-LAN circuit, communication stops. Accordingly the audio system does not function normally.
   • When audio system is not equipped with a navigation system, audio head unit is the master unit. (When audio system is equipped with a navigation system, navigation ECU is the master unit.)
   • The car audio system using AVC-LAN circuit has a diagnosis function.
   • Each product has its own specified numbers called physical address. Numbers are also allotted to each function in one product, which are called logical address.

Error codes over tuner and connected equipment are displayed on the screen of tuner.

1. Starting and Finishing Diagnosis Mode

   With the audio system OFF and the ignition switch in ACC, while simultaneously pressing the preset buttons "1" and "6", push "DISC" or "CD" 3 times.

   HINT:

   • A beep sound 3 times and the system goes on to the Service Check Mode.
   • System check and diagnosis memory check is performed in the Service Check Mode and the check result is displayed in ascending order of the component codes.
   • It may take about 40 sec. to complete these checks.
     Fig 9: Displaying Screen Of Tuner

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2. Displaying Result in Service Check Mode (For checking the system condition at present and in the past)
   1. By the "SEEK" switch operation, confirm the check result of each component.
      Fig 10: Displaying Result In Service Check Mode

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      Code No. (physical address) List 

      CODE CHART
      
      

      Code No. (physical address)	Equipment name
      190	Radio receiver assembly (Audio head unit)
      440	Power amplifier

   2. If "CHEC" or "ECHm" is detected in a component, activate the Detail Display mode and check its DTC.
   3. To restart the Service Check, press the preset button "1".
   4. To exit the diagnosis mode, press "DISC" or "CD" for 2 sec. or more, or turn the ignition switch OFF.
3. DISPLAYING RESULTS

   Results for each check are displayed as follows:

   ( ): Meaning

   • good (Normal)

     No DTC is detected for both "System Check Confirmation" and "Diagnosis Memory Response".

   • nCon(No connection)

     Although identified by the system at the time of registration, it has transmitted no response when the diagnosis mode is started.

   • CHEC(Check)

     If this is displayed, activate the Detail Display Mode and Check the DTC.

   • ECHn(Exchange)

     -ditto-

   • OLd (Old Version)

     An old version diagnosis system applies to this component.

   • nrES (No Response)

     In spite of response identified when the diagnosis mode is started, no diagnostic information has been responded.

4. Detail Display Mode (For displaying DTC of erratic components)
   1. While "CHEC" or ECHn" is displayed, press the preset button "2" to go on to the Detail Display Mode.
   2. By the "SEEK" switch operation, "the system check result (SYS)" and "the diagnosis memory response result (COdE)" can be displayed.
   3. Refer to the diagnosis code list and inspect the defective part(s).
   4. Press the preset button "3" to return to the Service Check Mode.
5. Service Check Mode
   Fig 11: Displaying Service Check Mode

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6. DISPLAY IN DETAIL DISPLAY MODE
   DISPLAY IN DETAIL DISPLAY MODE
   
   

   Segment for DTC	Meaning	Display Order by "SEEK UP" button operation (Reverse order when operating "SEEK DOWN" button)
   Sys	System check result	Physical address --> DTC
   COdE	Diagnosis memory response result	Physical address --> DTC --> Auxiliary code --> Connection check number --> Number of occurrence

7. Deleting DTC memory (Deleting DTC stored in the past) 
   1. After repairing defective part(s), start the diagnosis mode.
   2. Press the preset button "5" for 2 sec. or more. (Display: "CLr")

      HINT:

      When DTC memory is completely deleted, a beep sounds once.

   3. Pressing the preset button "1", perform the Service Check again and confirm that no error is displayed for all component codes.

Physical address 440 Power amplifier

Physical address 190 Radio receiver assembly