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

D1-D4:

D4-D5:

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

To enable the THX(R) amplifier, the audio unit 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 THX(R) amplifier modifies the voltage signal from the audio unit. In the event of an overload, the audio unit 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 audio unit:
- Less than 0.4 volts: amplifier disabled
- Between 3.8 and 6.7 volts: amplifier enabled
- Greater than 8.5 volts: amplifier clipped

Possible Causes
- Fuse
- Circuitry
- THX(R) amplifier
- Audio unit