Bose Life CD5 Series I Service Manual page 15

THEORY OF OPERATION
U103's output signal is buffered by U105, and is fed to the A and B outputs. These outputs are
independently mutable through transistors Q103-106 and Q203-206. Each pair of transistors
provides approximately 80dB of attenuation when muted. These mute transistors are con-
trolled by the signals on J9-7 and J9-8. U103's output signal is also routed to headphone
amplifier U104. This provides gain and buffers the signal in order to drive a low impedance
load. When the headphones are inserted into J104, the control signal on J105-3 causes the A
speaker output to be muted.
The TAPE output jack functions like the FIXED output does. There is one exception. The TAPE
output is shut off whenever "TAPE" is selected as the source. This prevents feedback through
the TAPE deck if it was placed in "Record" while "TAPE" was selected as the source. This is
accomplished by feeding the FIXED level output signal from U102, pins 1 and 14 back into
U101. A control signal from U402 allows U101 to pass this signal to its outputs on pins 5 and
17, except when "TAPE" is selected as a source.
The FIXED, TAPE, and headphone outputs all have a single mute transistor which is used to
prevent pops and clicks during power-up and power-down. These transistors are all controlled
by the signal on J9-6. Each transistor provides about 40dB of attenuation when the muting is
switched on.
CD Player
The CD circuitry consists of six major sections: Analog signal processor (ASP) U501, digital
signal processor (DSP) U502, digital to analog converter (D/A) U506, CD microcontroller (µC)
U505, power drivers U503 and U504, and the CD mechanism. U501 contains the RF amplifier
and servo control circuits. U502 performs EFM demodulation, CIRC decoding, and outputs the
digital audio to U506. It also extracts the subcode Q information (track #, time, etc.) and con-
trols U501 during track access. U505 receives and interprets the subcode Q data from U502
and sends it along to U402. It also issues commands to U502 for track access, and controls all
operations of the CD circuitry.
U501 receives its input signal (through P501) from the mechanism's photo diode pickup. The
A, B, C, and D inputs are added together and amplified. The RF amplifier output appears on
RFSM (U501, pin 72 ). This signal is the familiar "eye pattern." This signal is sent to EFMIN on
U502, Pin 8 where it is sliced for EFM demodulation. The inverted and non-inverted sliced
outputs appear on the EFMO and EFMO~ lines (U502, pins 6 and 7) . These signals are low-
passed and subtracted and the output appears on SLCO (U501, pin 53). This signal supplies
the DC bias for the RFSM signal. This signal is then sent to the slicer for slice level control.
The RFSM signal is peak-detected and compared to a reference to determine if there is a
signal being received back from the disc. The output appears on DRF (U501, pin 40 ). This
signal is used by U505 to determine if the lens is in focus. The envelope of the RFSM signal is
also used in determining when the laser crosses a track boundary during track access. The
HFL signal (U501, pin 48) conveys this information to U502.
The A+C signal is subtracted from the B+D signal. This produces the focus error signal FEAO
(U501, pin 26 ). The focus gain is adjusted by R527. This signal is amplified and filtered by the
focus servo amplifier (inside U501). It then appears as an output at FDO (U501, pin 22). The
FDO signal is fed to U503. U503 generates the complementary outputs (pins 11 and 14) that
are used to actuate the focus coil (P502, pins 5 and 8).
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