Radio/Audio System Description and Operation
Radio/Audio System Description and Operation
Contents
* RPO options
* Circuit description
* Component description
* Theft deterrent feature
RPO Options
The entertainment system on this vehicle is configured with either a base or uplevel audio system. Both the base and uplevel audio systems contain a radio, antenna, and speakers. The following shows the Entertainment RPOs that are available for this vehicle:
* (U1C) AM/FM Stereo CD
* (US8) AM/FM Stereo, CD, MP3, RDS, EQ
* (US9) AM/FM Stereo, 6-Disc CD, MP3, RDS, EQ
* (UW5) Base 6 Speaker
* (UQ3) Uplevel 6 Speaker
* (U2K) Digital Radio
Circuit Operation
Radio Power
The main radio power is supplied by a 15A RADIO fuse located in the body control module (BCM). The radio does not require a discrete ignition feed circuit for power moding. The power moding is accomplished using a structure of Virtual Networks (VN). The Power Mode Master (PMM) transmits the GMLAN power mode signals.
The radio supports the following signals:
* System Power Mode
* Infotainment Operation Allowed
The radio also supports the following GMLAN Vehicle Power Modes:
* OFF
* ACCESSORY
* RUN
* CRANK REQUEST
Radio Ground
A wire in the main radio connector that is connected to battery negative at all times provides the main radio ground. Resistance between the ground pin and the vehicle battery negative terminal must not exceed 0.05 ohms.
Radio Speaker Outputs
At low volume, the plus (+) and minus (-) speaker outputs circuits measure approximately 7-8 volts. If a plus or minus circuit for any speaker output is shorted to ground or voltage, the radio disables the circuit for component protection and sets a diagnostic trouble code (DTC). The radio sets the speaker circuit DTC on non-amplified systems only. As the radio volume increases the voltage on the plus and minus circuits change to create a voltage difference between each other. The difference in voltage is what drives the voice coil of the speaker producing sound.
Radio Head Unit Dimming
GMLAN signal data received by the radio determines the radio dimming and backlighting levels. The radio sets the backlight and vacuum fluorescent (VF) display dimming to the value indicated by the interior dimming level and interior dimming display level signals in the GMLAN dimming information frame. The radio provides faceplate and control/graphics backlighting in the OFF (RAP inactive) when the exterior lighting VN is activated. The radio display is consistent then with the surrounding devices that use analog pulse width modulation (PWM) dimming to backlight their control/graphics when the power mode is OFF and the park lights are ON.
Amplifier Interface
A discrete switched 12-volt output is used to control the power-state of the amplifier. To respond quickly to audio input and control signals, the amplifier is ON in all vehicle power modes except OFF and CRANK Request. However, when the amplifier is deactivated it still must allow chime functionality. The internal amplifier bridges are fully powered and unmuted when the amplifier receives the switched 12-volt input.
The radio provides a remote radio control signal to control overall muting of the amplifier. The amplifier receives PWM signals on the circuit at varying duty cycle percentages for controlling the muted and unmuted functions of the amplifier.
The function table below shows the 4 possible amplifier mute functions.
Amplifier Radio Speaker Inputs
The low-level audio signals (LF, RF, LR, and RR) from the radio are the inputs to the amplifier. The amplifier boosts these inputs and outputs them to the vehicle speakers. If one speaker plus or minus low level audio signal circuit is open between the radio and the amplifier, the input to the amplifier is approximately half. The speakers for that channel then operate at approximately half the normal volume or in some cases no volume.
The low level audio signals from the radio to the amplifier typically measure in the 4-5 volt range.
Amplifier Speaker Outputs
At a low volume, the plus (+) and minus (-) speaker outputs circuits measure approximately 2-7 volt AC or 7-8 volt DC at the speaker connector when testing a normal working system. If a plus or minus for any speaker output is shorted to ground or voltage, the amplifier circuitry will turn OFF the front outputs or rear outputs for component protection.
Repeat speaker failure can be caused by a damaged amplifier. Test for a damaged quad bridge output in the amplifier if the wiring between the amplifier and speaker test negative for a short to voltage. Prolonged exposure to DC voltage can cause a speaker coil to short. An early indication of a shorted speaker coil is distortion/noise and eventual failure.
Component Description
Antenna System
The antenna system receives broadcast AM or FM stereo signals from free space and sends the signals to the radio receiver for processing via a coaxial antenna cable. Good antenna grounding is important for good radio reception.
Radio
The operator interfaces with the radio system through the radio display and controls. Through these controls the operator is able to control system power, volume, fade, balance, bass, and treble equalizations. Control on the integrated CD, MP3, or XM Satellite Radio system is also available when equipped with these options. A VFD (vacuum florescent display) provides system feedback to the operator.
The radio processes the AM and FM signals from the antenna system or the information from the CD media, amplifies that information and sends the output to the speaker system.
The radio is located in the instrument panel center stack area and is fastened to the instrument panel by fasteners. A rear bullet type guide pin is provided to aid in aligning the radio. An electrical connection to the radio is a 30-way connector that is part of the I/P harness, antenna lead connector, and an additional 16-way harness connector is present on OnStar(R) equipped vehicles. Additional service length is provided in the radio harnesses to allow connection prior to radio installation.
Radio amplifier outputs to the speakers are protected from damage should speaker leads become shorted to ground or shorted to vehicle power. The radio will sense these conditions and shut down the amplifier outputs in a non-destructive manner. After the short condition is removed, the radio will return to normal operation.
Speakers
The speaker system consists of 6 speakers, two 6 inch speakers mounted in the doors, two 3.5 inch speakers mounted in the back panels, and two one-inch tweeter speakers mounted in the A-pillars. The amplified speaker system adds a subwoofer and amplifier.
Auxiliary Jack Socket
The AM/FM Stereo CD radio shall provide a 3.5 mm Auxiliary stereo jack that will allow playback of audio signals from remote devices (e.g., portable tape player, IPOD, MP3 playback device, etc.).
OnStar(R)
OnStar(R) equipped (RPO UE1) vehicles use the radio and speaker system for voice communication from the OnStar(R) operator to the vehicle. Voice communication from the vehicle to the OnStar(R) operator is through the OnStar(R) microphone and module, which is not a part of the radio system.
The radio receives a mono audio signal from the VCIM via two cellular telephone voice signal circuits. When OnStar(R) begins operation, the non-OnStar(R) radio audio is muted and the fade control is adjusted to the full front speakers. OnStar(R) audio then can be heard over the vehicle front speakers. The radio volume control can then be used to adjust the volume to a desired level.
Theft Deterrent
The radio theft deterrent system is intended to disable radio functionality if incorrect vehicle information is received by the radio. The radio disables functionality if the VIN information received by the radio does not match the VIN information that has been learned by the radio. A VIN sequence is the last 6 digits of the VIN. The radio receives this information in a GMLAN frame form.
The radio shall provide the following theft operating modes as part of the radio theft deterrent system:
* No VIN Mode-A radio that has not received or learned a VIN. In this mode the radio has limited functionality.
* Normal Mode-A radio has received a VIN sequence. The radio only learns the VIN sequence if the VIN sequence contained all 6 digits. In this mode the radio has full functionality.
* Theft Detected Mode-A radio that had previously learned a VIN sequence and subsequently received a VIN sequence not matching the learned sequence. In this mode the radio has limited functionality.
AM/FM Reception
Radio Signal
The radio signal is sent from a broadcast station and is then received by an antenna. The strength of the signal received depends on the following:
* The power output, or wattage, of the broadcasting station
* The location of the vehicle, or receiver, relative to the broadcast tower
* Obstacles between the tower and the receiver
* Atmospheric conditions
* Which band, AM or FM, the station is broadcasting
* Type of antenna and the ground plane
AM Reception
The AM band has a lower frequency range than the FM band. These longer wavelengths:
* Bend around obstacles
* Follow the curvature of the earth
* May reflect, or skip, off of the ionosphere
The AM frequencies have longer range due to the ground wave. The ground wave follows the curvature of the earth and is affected by its conductivity. Greater conductivity equates to less signal loss, thus transmission over water is better than over land. The AM band has a range of 80-320 km (50-200 mi).
FM Reception
The shorter wavelengths of the higher frequency FM band:
* Reflect off obstacles
* Are absorbed by the ground
* Penetrate the ionosphere
Broadcasts in the FM band are limited to "line of sight" reception which is typically 40 km (25 mi). Even when out of a direct line of sight, the signal may be reflected into areas that would be in a "shadow" otherwise. Factors which affect the line of sight include:
* Height of the broadcast antenna
* Height of the receiving antenna
* Terrain and buildings in the broadcast path
XM Reception
XM satellite radio provides digital radio reception. The XM signal is broadcast from two satellites and, where necessary, terrestrial repeaters. The high power satellites allow the antenna to receive the XM signal even when foliage and other partial obstructions block the antennas view of the satellite. Terrestrial repeaters are used in dense urban areas. These repeaters will receive the satellite signal and re-broadcast them at much higher power levels in order to ensure reception in areas with densely packed tall buildings.
XM Satellite Radio
XM(TM) is a satellite radio service that is based in the 48 contiguous United States and Canada. XM(TM) offers a large variety of coast-to-coast channels including music, news, sports, talk, traffic/weather (U.S. subscribers), and children's programming. XM(TM) provides digital quality audio and text information that includes song title and artist name. A service fee is required in order to receive the XM(TM) service. For more information, contact XM(TM); In the U.S. at www.xmradio.com or call 1-800-852-XMXM (9696) or in Canada at www.xmradio.ca or call 1-877-GET-XMSR (438-9677).
Digital Radio Receiver
The radio controls communicate with the digital radio receiver via the serial data communication circuit. The digital radio receiver sends remote radio audio signals to the radio.