Bose AV28 Manual page 9

2.6 Troubleshooting
Verifying functionality of the power supply system by measuring the DC levels on each supply
(including the power pack) is sufficient for basic troubleshooting.
If power supply problems are suspected, or if DC levels on the supplies are incorrect, evaluate
and correct these parameters with no power applied:
•
Check continuity between J104 and pin 8 of each supply.
•
Measure the resistance of R321 on the Tuner PCB.
• Measure the resistance of feedback resistors (R304 and R305 in the +12V supply) in each supply.
•
Verify that no supply voltage output is shorted to ground.
3.0 Control Electronics
The majority of the control electronics are located on the Main PCB, the notable exceptions being
the Infrared Blaster diodes and receiver module (located on an auxiliary PCB under the DVD-ROM
drive tray) and the RF transceiver circuitry (located on the Tuner PCB).
3.1 Processor
U1 is a CS98000 DVD decoder IC that also functions as the media center's main processor.
U1 contains two built-in 32-bit RISC processors, a DSP core, a memory interface which supports
SDRAM and FLASH ROM, an ATAPI interface, a DMA controller, an MPEG video decoder, on-
board data and instruction caches, a digital video interface, digital audio processing, a general
purpose interface, and numerous general-purpose I/O.
One RISC processor in U1 (RISC0) manages the ATAPI interface to the DVD-ROM drive, and
handles all low-level details associated with playback/navigation of DVD and CD discs. RISC0
sends standard ATAPI control commands to the drive and receives MPEG-compressed audio,
video, and control information back. It decodes the MPEG information from the DVD-ROM drive on
the ATAPI bus and stores the decoded video into SDRAM for later readout to the video interface. It
also oversees the onboard DSP core, as required, when decoding digital audio data, and sends it
out the digital audio interfaces.
The second RISC processor (RISC1) runs Bose
sembles VFD and On-Screen Display (OSD) information, and controls I/O functions including
reading the console buttons, receiving the RF and IR remote control commands, driving the OSD
and VFD display on the console, controlling the AM/FM tuner sub-circuit, and driving the IR blaster
controls.
Connections to U1 are made throughout SD254135.
Theory of Operation
® software that handles system control, as-
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