Audio System: Description

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

Fig 1: Radio Wave Band Broadcasting Table

SERVICE AREA
There are great differences in the size of the service areas for AM and FM broadcasts. Sometimes FM stereo broadcasts cannot be received in an area where AM broadcasts can be received very clearly.

Fig 2: Identifying FM & AM Service Areas
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Not only do FM stereo broadcasts have the smallest service area, but it also picks up static and other types of interference ("noise") easily.
RECEPTION PROBLEMS
Besides static, there are also problems called "fading", "multi-path" and "fade out". These problems are not caused by electrical noise but by the nature of the radio waves themselves.
1. 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 radio waves that reach the vehicle's antenna directly. This type of interference is called "fading".
  
  Fig 3: Identifying Fading Interference
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Multi-path:
  One type of interference caused by bounce of radio waves against obstructions is called "multi-path". Multi-path occurs when a signal from the broadcast transmitter antenna bounces off buildings and mountains and interferes with the signals that reach the vehicle's antenna directly.
  
  Fig 4: Identifying Multi-Path Interference
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
3. 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 out as the vehicle goes behind buildings or other obstructions. This is called "fade out".
  
  Fig 5: Identifying Fading Out Of FM Signal Due To Obstructions
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
NOISE PROBLEMS
1. Questionnaire for noise:
  For noise troubleshooting it is very important to understand the customer's claims. Use the questionnaire in Fig 6 and diagnose the problem accurately.
  
  Fig 6: AM/FM Noise Symptom Table
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  
  HINT:
  
  In the case that the noise occurrence condition does not meet any of the above, check based on the "Trouble Phenomenon". Refer to multi-path and fading.
2. Matters that require attention when checking:
  - Noise coming into the radio usually is negligible. The radio has noise protection and extremely loud noise is unlikely. When extremely loud noise comes into the radio, check if the grounding is normal where the antenna is installed.
  - Check if all the regular noise prevention parts are properly installed and if there is any installation of non-authorized parts and non-authorized wiring.
  - If you leave the radio out of tune (not tuning), it is easy to diagnose the phenomenon as noise occurs frequently.
COMPACT DISC PLAYER
Compact disc players use a laser beam pick-up to read the digital signals recorded on the CD and reproduce analog signals of the music, etc.

HINT:

Never attempt to disassemble or put oil on any part of the player unit. Do not insert any object other than a disc into the magazine.

NOTE: CD players use an invisible laser beam which could cause hazardous radiation exposure. Be sure to operate the player correctly as instructed.
Tape player/head cleaning: MAINTENANCE
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 7: Cleaning Tape Player/Head
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
CD player/disc cleaning: MAINTENANCE
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.

NOTE: Do not use a conventional record cleaner or anti-static preservative.

Fig 8: Cleaning CD Disc With Soft Cloth
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
OUTLINE OF AVC-LAN
1. What is AVC-LAN?
  AVC-LAN 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 signals, visual signals, signals for switch indications and communication signals.
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 to audio systems customers that need has been upgraded. These led to the creation of this standardization.
  
  The concrete objectives are explained below.
  1. When products made by different manufactures were combined together, malfunctions often occurred (for example, sound did not come out). This problem has been resolved by the standardization of signals.
  2. Various types of aftermarket products have been able to be added or replaced freely.
  3. Because of (2) above, each manufacture has become able to concentrate on developing products in their strongest field. This has enabled many types of products to be provided inexpensively.
  4. Before, a new product developed by a manufacturer could not be used due to a lack of compatibility with other manufactures products. With the new standard, users can enjoy new products without incompatibility.
3. The above descriptions are the objectives introduced by AVC-LAN. By this standardization, development of new products will no longer cause systematic errors. Thus, this is a very effective standard for future products.
  HINT:
  - When +B short or GND short is detected in the AVC-LAN circuit, communication stops. Accordingly the audio system does not function normally.
  - When an audio system is not equipped with a navigation system, the audio head unit is the master unit. When an audio system is equipped with a navigation system, the radio receiver is the master unit.
  - A car audio system using the AVC-LAN circuit has a diagnosis function.
  - Each product has its own specified numbers called physical addresses. Numbers also allotted to functions in a product, are called logical addresses.