Bose AV28, Manual

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13
Theory of Operation
3.3.2.2 Infrared Blaster Diodes
Four diodes located on the IR PCB transmit infrared messages to external A/V equipment. U704
provides the modulated data for the diodes; Q703 and Q706 supply the +5V drive voltage, and
R729 and R730 on the Main PCB limit the IR transmit current (setting the transmit brightness).
3.3.2.3 IR Emitter
For situations where the position of the AV28 does not allow its built-in IR Blaster signals to prop-
erly control an external product, a supplemental IR Emitter “dongle” can be plugged into the back of
the media center and pointed more directly at the equipment in question. This “dongle” is essentially
a combination cable and IR-transmitter diode, and plugs into the jack labeled “IR Emitter (J704).”
Q703/Q705 provide the +5V drive voltage for the dongle, and R739/R740 limit the drive current to
about 50mA.
3.3.2.4 Infrared Receiver Module
The IR PCB contains an infrared receiver module. This module allows the media center to be
controlled by any IR remote control capable of sending Bose
® AV28 IR commands (NOTE: Re-
ceive IR needs to be enabled via the System Setup menus in the OSD first, however). The Main
PCB su5.1V to the module. The module performs light filtering functions, optical to electrical
conversion, demodulation about a 38-kHz carrier, and level shifting to provide TTL-level outputs to
U1. The plastic housing surrounding this area is translucent to infrared. Infrared control must be
enabled in the OSD to be functional.
3.3.2.5 Infrared Troubleshooting
During the Power-On Self-Test (POST) phase, the console attempts a query of the IR Blaster IC
and an infrared loopback test; TAP query and the console keypad provide access to test results.
If the IR Blaster IC query fails, concentrate troubleshooting efforts on U704 on the Main PCB.
Symptoms of successful queries to the IR Blaster IC and failed loopback tests require trouble-
shooting of the IR PCB. First, verify cable placement and integrity. Verify basic receiver module
functionality by injecting an infrared signal (for example, a Bose Wave Radio remote) and measur-
ing pin 3 of J1000 on an oscilloscope. To test basic transmitter functionality, verify diode conduction
and orientation, then issue TAP commands to control a Bose Wave Radio.
Troubleshooting customer complaints regarding control integration exceeds the scope of this
document.