Test D: Poor Quality/Distorted/No Sound From All Speakers - THX(R) Audio System

PINPOINT TEST D: POOR QUALITY/DISTORTED/NO SOUND FROM ALL SPEAKERS - THX(R) AUDIO SYSTEM

Normal Operation
The THX(R) amplifier receives voltage through circuits SBP38 (BN/RD) and SBP18 (YE/RD), and ground through circuit GD148 (BK/YE).

Left and right channel audio signals are sent from the audio control module (ACM) to the audio digital signal processing (DSP) module through circuits VME07 (WH), RME07 (WH/BN), VME10 (WH/VT), and RME10 (WH/OG). If there is a fault on one of these circuits, the audio quality will be reduced by approximately 25% for all speakers.

To enable the DSP module, the ACM sends voltage through the enable/clip circuit SME23 (VT/RD). The circuit acts as both an output (to enable the amplifier) and an input (to detect an amplifier overload condition). A variable resistor in the DSP module modifies the voltage signal from the ACM. In the event of an overload, the ACM clips the audio output signal to the amplifier (heard as distortion), in order to prevent damage to the amplifier and speakers.

The clip/enable status is based on the following voltages, as detected by the ACM:
- Less than 0.4 volts: amplifier disabled
- Between 3.8 and 6.7 volts: amplifier enabled
- Greater than 8.5 volts: amplifier clipped

NOTE: Despite their names, DTCs B2925 and B292A apply to the DSP module clip/enable circuit, not to the subwoofer.

- DTC B2925 (Subwoofer Speaker Short Circuit) - sets with DTCs B2965 and B292A when a short to ground is detected in circuit SME23 (VT/RD).
- DTC B292A (Subwoofer #2 Speaker Short Circuit) - sets when an open or short to ground is detected in circuit SME23 (VT/RD). If an open is detected, DTC B2965 will also be set. If a short to ground is detected, DTCs B2965 and B2925 will also be set.
- DTC B2965 (Audio System Speaker Circuit Fault) - sets when an open or short to ground is detected in circuit SME23 (VT/RD).

This pinpoint test is intended to diagnose the following:
- Fuse
- Wiring, terminals or connectors
- DSP module
- ACM

D1-D4:

D5-D7:

D8-D10: