Section 439 (Audio System - Diagnostics): Description

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

Fig 1: Identifying Radio Wave Band Chart

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1. There is a great difference in the size of the service areas for AM and FM broadcasting. Sometimes an FM stereo broadcast cannot be received even though AM can be received very clearly.

   FM stereo has the smaller service area, and it also picks up static and other types of interference ("noise") easily.

   Fig 2: Identifying Service Area

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HINT:

Besides the problem of static, there are other problems, such as "phasing", "multipath" and "fade out". These problems are caused not by electrical noise but by the nature of the radio waves themselves.

1. Phasing

   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 that reach the vehicle's antenna directly from the same transmitter. This type of interference is called "phasing".

   Fig 3: Identifying Phasing

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2. Multipath

   Interference caused by reflection of radio waves against obstructions is called "multipath". Multipath occurs when radio signals emitted from the broadcast transmitter antenna are reflected against tall buildings or mountains and interfere with other signals which are to be received directly.

   Fig 4: Identifying Multipath

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3. Fade Out

   FM radio wave tends to be reflected against obstructions such as tall buildings or mountains because FM frequency is higher than AM. For this reason, FM signals often seem to gradually disappear or fade away as the vehicle goes behind those obstructions. This phenomenon is called "fade out".

   Fig 5: Identifying Fade Out

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1. It is very important for technicians to clearly understand a customer's claim about noise. Use the following table to diagnose the phenomena.
   NOISE PROBLEMS CHART
   
   

   Radio wave	Condition in which noise occurs	Probable cause
   AM	Noise occurs at a specific place.	Strong possibility of foreign noise.
   AM	Noise occurs when listening to faint broadcasting.	The same program may be broadcasted from some local stations. If the program is the same, one of those may be tuned in.
   AM	Noise occurs only at night.	Strong possibility of an interfering beat from a distant broadcasting.
   FM	Noise occurs at a specific place during driving.	Strong possibility of multipath noise and phasing noise caused by changes of FM frequency.

   HINT:

   If the condition when the noise occurs does not meet any of the above, find out the cause based on "Reception Problems". Refer to the description about multipath and phasing mentioned previously.

1. Compact Disc (hereafter called "CD") players use a laser beam pick-up to read the digital signals recorded on CDs and reproduce analog signals of the music, etc. 4.7 in. (12 cm) and 3.2 in. (8 cm) discs are available for the CD player.

   HINT:

   Never disassemble or apply oil to any part of the player unit. Do not insert any object other than a disc into the CD player.

   NOTE: CD players use an invisible laser beam which could cause hazardous radiation exposure. Be sure to operate the player correctly as instructed.

1. Raise the cassette door with your finger.

   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: Cleaning Tape Player/Head

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

Fig 7: Cleaning Player/Disc

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1. What is AVC-LAN?

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

   The unified standard includes signals, such as audio, visual and signals for switch indication and communication.

   Fig 8: Outline Of AVC-LAN Flow Chart

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2. Objectives

   Recently development in car audio systems has been rapid 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 customers want to upgrade their audio systems. This is the factor that lies behind this standardization.

   The concrete objectives are explained below.

   1. When products by different manufacturers were combined together, malfunctions such as sound failure occurred. This problem can be solved by standardization of signals.
   2. Various types of after market products are available.
   3. Because of the above (2), each manufacturer has been able to concentrate on developing products in their strongest field. This has enabled the development of inexpensive products.
   4. In general, a new product developed by a particular manufacturer could not be used due to a lack of compatibility with other manufacturer's products. By developing this new standard, users can enjoy a range of compatible products from different manufacturers.

   HINT:

   • When a short to B+ or short to ground is detected in the AVC-LAN circuit, communication stops, and the audio system will not function normally.
   • When the audio system is not equipped with a navigation system, the audio head unit is the master unit. When the audio system is equipped with a navigation system, the multi-display is the master unit.
   • The radio receiver assy is equipped with a resistor (60 to 80 Ω) for communication.
   • The car audio system using the AVC-LAN circuit has a diagnostic function.
   • Each unit has its own specified number called a physical address (three-digit number). Numbers are also allotted to each function, which are called logical addresses (two-digit number).

1. Components in the audio system communicate with each other through the AVC-LAN. (Radio receiver with CD changer control function)
2. The master component of the AVC-LAN is the radio receiver assy with a resistor (60 to 80 Ω), which is necessary for communication.
3. When a short circuit or circuit breakdown occurs in the AVC-LAN circuit, the audio system will not operate normally due to the communication cutoff.

1. The audio system has a diagnostic function (The diagnostic result is displayed on the LCD of the radio receiver assy). (Radio receiver with CD changer control function)
2. The component code (physical address), or three-digit number (in hexadecimal) is set for each component comprising the AVC-LAN.
3. The logical address, or two-digit number (in hexadecimal) is set for each function and component unit in each component.
   Fig 9: Identifying Diagnostic Function

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