Part 2

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.

The antenna base and mast should be installed to the torque specifications provided in the Antenna Replacement - Digital Radio procedures.

The antenna mast is a single 1/4 wave design located at the right front fender.

Ground Strap
The braided ground strap, which is connected between the radio case and the instrument panel fuse block (IPFB), is provided to improve reception and deter noise from entering the audio system.

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 vacuum florescent display (VFD) 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 I/P center stack area and is fastened to the I/P by 2 fasteners. Guide pins are provided to aid in aligning the radio. Electrical connections to the radio are a 24-way connector from the I/P harness, antenna lead connector and braided ground strap. An additional 12-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.

Clock time is displayed continuously on the UM7 and U1C radios when the ignition is OFF. Pressing the RCL provides momentary backlighting. Time is not displayed on the US8 and US9 radios when the ignition is off. Pressing RCL will temporarily display the time.

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 4 speakers, mounted in the doors. The optional speaker system (RPO UQ6) includes an additional speaker mounted in the front driver and passenger door mirror trim panel. The premium audio system (RPO WBM) adds a subwoofer and amplifier.

OnStar(R)
OnStar(R) equipped (RPO UE1) vehicles use the radio amplifier 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.

When OnStar(R) begins operation, the radio volume is set to a preset level, autotone preset for OnStar(R) becomes active and the fade control is adjusted to the full front speakers. The radio volume control can then be used to adjust the volume to a desired level.

The radio system and OnStar(R) system are connected through the 12-way connector at the back of the radio. Left and right channel OnStar(R) audio, mute control of radio functions by OnStar(R), and the audio signal ground are the circuits provided in the 12-way connector.

Disconnecting the 12-way connector from the radio will isolate the radio system from the OnStar(R) system. Voice communication from the vehicle to the OnStar(R) operator could be possible under this condition. However, the vehicle occupant will not be able to hear the OnStar(R) operator.

For more information regarding radio operation problems, refer to Symptoms - Radio, Stereo, and Compact Disc and Diagnostic Starting Point - Radio, Stereo, and Compact Disc. For further information regarding OnStar(R) operation, refer to OnStar Description and Operation in Cellular Communication.

Amplifier
Vehicles equipped with Premium Audio (RPO WBM) include an amplifier. The amplifier has low level inputs from the radio for the 4 speaker channels and amplifies the sound. The amplifier receives a radio ON signal from the radio. This signal is delayed momentarily at initial key on to prevent any speaker pops during start-up.

The purpose of an amplifier is to increase the power of a voltage or current signal. The output signal of an amplifier may consist of the same frequencies as the input signal or it may consist of only a portion of the frequencies of the input signal, as in the case of a subwoofer or a mid-range amplifier.

Subwoofer
The premium audio system includes a subwoofer, which is mounted in the rear of the vehicle. The subwoofer is a single speaker, designed for low frequency response. The subwoofer speaker is a dual coil design. The amplifier, which is included with the RPO WBM premium audio package amplifies the low frequency and outputs it to the subwoofer.