Theory Of Operation - Bose Life CD5 Series I Service Manual

THEORY OF OPERATION

Overview
The Lifestyle ® Model 5 music center is a self-contained CD player, AM/FM tuner, preamplifier,
®
and control center for use with Bose powered speaker systems. In addition to the two internal
sources (CD and tuner), it also allows for up to three external devices to be connected (i.e.
AUX, VIDEO, and TAPE). It uses a Radio Frequency (RF) remote control that allows the unit to
be operated from different rooms within a house without the need for a line-of-sight path back
to the console. The remote control commands for the external sources are translated and
passed to the serial data output jack. With the CE-I accessory device this data can be con-
verted to Infrared (IR) for use with many conventional audio devices.
Power Supply
The unit is powered by an external 12VAC power supply capable of delivering 1.2 amps rms.
Dl, C2, D2, and C6 form positive and negative half-wave rectifiers respectively. Q1, Q2, Q3,
and their respective components make up a discrete low dropout regulator with a nominal
output voltage of 10. 2V. VR1 is the corresponding negative voltage regulator with an output of
-12V. These two regulators create the bipolar supply used by all of the audio circuits. The
supply is turned on and off with the unit by the control signal on J7-10.
R5, D3, C9, and VR2 create an +8V regulated supply that is used by the CD servo circuits and
the remote RF receiver. R6, D4, C11, and VR3 create a +5V regulated supply that is used by
the main and CD microcontrollers (U402 and U505), and the CD control circuits (U501, U502,
etc.). Both supplies are live at all times. R5 and R6 limit the power dissipation of their respec-
tive regulators. VR2 and VR3 normally run quite hot to the touch.
R8, D6, and C13 form an unregulated supply (M+) that is used by the CD drive electronics.
C14, D7, D8, and C15 form a charge pump that creates a negative high voltage. This voltage
is regulated down to -24V by R9, D9, and C16. The vacuum fluorescent display (VFD) driver
U403 uses this -24V to shut off segments in the display. C19 and C18 reduce the 12VAC to
approximately 3Vrms. This voltage powers the display's (VFD401) heater. C16, D10, C17, and
R10 provide a DC bias of -15V for the VFD heater (cathode).
Control Electronics
Main microcontroller (µC) U402 controls the audio circuits, tuner, display, and push buttons.
The µC runs at a nominal frequency of 4.0MHz that is supplied by ceramic resonator X401.
The µC is reset by a rising edge on pin 1 caused by R409 and C404. This occurs automatically
on power-up but may be forced manually by depressing S416 (if installed).
U402 communicates with U403 over a four wire serial data bus (U403, pins 15, 16, 18 and
19). The bus is updated once per millisecond. U403 latches the serial data into its outputs,
driving the VFD. The VFD is a four grid multiplexed display with 16 anodes at each grid. The
grids are turned on sequentially, one each millisecond. As each grid is turned on, the corre-
sponding anodes for that grid are also turned on. This lights the desired segments. When the
next grid is turned on, the anodes are changed to correspond to the desired segments under
this next grid. In this way, the entire display is scanned, 1/4 at a time. The display is blanked for
a brief interval in-between when one grid is turned off and the next is turned on. In this blank-
ing interval, the push buttons are scanned to determine what keys are being pressed. This
data is read in on U402, pins 12 through 15.
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