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1、055ZX0530 kHz 300 kHz 3 MHz 30 MHz 300 MHzLF MF HF VHFAM FMFrequency modulationFrequencyDesignationRadio waveModulation Amplitude modulationBE2818FM (Stereo)FM (Monaural)AMBE2819FadinglonosphereDIAGNOSTICS AUDIO SYSTEM (April, 2003)05593758Author : Date :2004 COROLLA (RM1037U)AUDIO SYSTEM (April, 20
2、03)DESCRIPTION1. RADIO WAVE BANDThe radio wave bands used in radio broadcasting are as follows:LF: Low FrequencyMF: Medium FrequencyHF: High FrequencyVHF: Very High Frequency2. SERVICE AREA(a) There are great differences in the size of the service areafor AM and FM broadcasting. Sometimes FM stereob
3、roadcast cannot be received even through AM can bereceived 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 PROBLEMSHINT:Besides the problem of static, there are also the problems called ”fadi
4、ng”, ”multipath” and ”fade out”. Theseproblems are caused not by electrical noise but by the nature of the radio waves themselves.(a) FadingBesides electrical interference, AM broadcasts are alsosusceptible to other types of interference, especially atnight. This is because AM radio waves bounce off
5、 the ion-osphere at night. These radio waves then interfere withthe signals from the same transmitter that reach the ve-hicles antenna directly. This type of interference is called”fading”.BE2820MultipathBE2821Fade Out05594DIAGNOSTICS AUDIO SYSTEM (April, 2003)759Author : Date :2004 COROLLA (RM1037U
6、)(b) MultipathInterference caused by reflection of radio waves againstobstructions is called ”Multipath”. Multipath occurs whenradio signals emitted from the broadcast transmitter an-tenna are reflected against tall buildings or mountainsand interferes with other signals which is to be receiveddirec
7、tly.(c) Fade OutBecause of the frequency higher than that of AM, FM ra-dio wave tends to be reflected against obstructions suchas tall buildings or mountains. For this reason, FM signalsoften seems to gradually disappear or fade away as thevehicle goes behind those obstructions. This phenome-non is
8、called ”fade out”.4. NOISE PROBLEMS(a) It is very important for noise troubleshooting to understand a customers claim clearly. Use the followingtable to diagnose the phenomenon.Radio wave Condition in which noise occurs Probable causeNoise occurs at a specific place. Strong possibility of foreign no
9、ise.AMNoise occurs when listening to faint broadcasting. The same program may be broadcasted from some local sta-tions. If the program is the same, one of those may be tunedin.Noise occurs only at night. Strong possibility of beat from a distant broadcasting.FMNoise occurs at a specific place during
10、 driving. Strong possibility of multipath noise and fading noise causedby changes of FM frequency.HINT:If the condition where the noise occurs does not meet any of the above, find out the cause based on ”Recep-tion Problems”. Refer to the description about Multipath and Fading mentioned previously.5
11、. COMPACT DISC PLAYER(a) Compact Disc (hereafter called ”CD”) Players use a laser beam pickup to read the digital signals re-corded on the CD and reproduce analog signals of the music, etc. There are 4.7 in. (12 cm) and 3.2in. (8 cm) discs available for the CD player.HINT:Never attempt to disassembl
12、e or oil any part of the player unit. Do not insert any object other than a disc intothe magazine.NOTICE:CD players use an invisible laser beam which could cause hazardous radiation exposure. Be sureto operate the player correctly as instructed.N17398Example:Head CapstanPinch RollerBE4331DIAGNOSTICS
13、 AUDIO SYSTEM (April, 2003)05595760Author : Date :2004 COROLLA (RM1037U)6. MAINTENANCETape Player/Head Cleaning:(a) Raise the cassette door with your finger.Using a pencil or similar object, push in the guide.(b) Using a cleaning pen or cotton applicator soaked in clean-er, clean the head surface, p
14、inch rollers and capstans.7. MAINTENANCECD Player/Disc Cleaning:If the disc gets dirty, clean the disc by wiping the surface fromthe center to outside in the radial directions with a soft cloth.NOTICE:Do not use a conventional record cleaner or antistatic pre-servative.8. COMMUNICATION SYSTEM(a) Com
15、ponents in the audio system communicate each other though AVCLAN.(b) The master component of AVCLAN is the radio receiver assy with a resistance (60 80 W ), whichis necessary for communication.(c) When short circuit or circuit breakdown occurs in the AVCLAN circuit, the audio system does not oper-at
16、e normally due to the communication cutoff.9. DIAGNOSIS FUNCTION(a) The audio system has diagnosis function (The diagnosis result is displayed on the LCD of the radioreceiver assy).(b) The component code (physical address), or threedigit number (in hexadecimal) is set for each com-ponent comprising AVCLAN.(c) The logical address, or twodigit number (in hexadecimal) is set for each function and component unitin each component.055ZY0505596DIAGNOSTICS AUDI
