Bose Lifestyle CD5 Series I, Service Manual

Page: 17 / 70

16
THEORY OF OPERATION
U505’s oscillator is obtained from a 4MHz ceramic resonator (X502). U505 is reset by a rising
edge on pin 1 that is caused by R573 and C574. This occurs automatically on power-up, but
may be forced manually by depressing S502 (if installed). U505 communicates with U502 on a
serial bus (U502, pins 50 through 54). U505 sends servo commands for focusing and track
access to U502. U502 sends subcode Q data to U505 which extracts track, time and table of
contents information from it. The time and track data is formatted, and is sent to U402 on a
serial bus (U505, pins 11-13).
During track access, U505 controls the sled motor directly using the FEED+ and FEED- lines
(U505, pins 21 and 22). It also directly controls the laser U503 and VCO using the LASER~
line (U505, pin 9). When the laser is turned on, the VCO and U503 are enabled, otherwise
they are turned off. U505 can also enable and disable U504 with the MOTOR_EN line (U505,
pin 20).
U506 (D/A converter) performs 8x oversampling and digital filtering. It then converts the digital
audio into left and right stereo outputs. D/A reference voltages are obtained from zener diode
D504. U506’s analog outputs are buffered by one-half of U507 (pins 5-7 and 8-10). The
buffered signal is lowpass filtered by the other half of U507. This removes any residual out-of-
band digital noise. The recovered audio is then routed to U101.
Tuner
The FM antenna signal is routed through F connector J301 and enters the FM front end mod-
ule. This contains a tuned RF amplifier, FM local oscillator, and a mixer. The IF output signal
appears on pin 4 (front end) and passes through 10.7MHz ceramic filter CF302. The filter’s
output is amplified by the IF gain stage. This stage consists of Q307, Q308 and their associ-
ated components. The signal is then passed through a second ceramic filter, CF303, a second
gain stage (Q309, Q310, etc.) and a third ceramic filter, CF304.
CF304’s output signal is sent to the main tuner IC, U301. This device contains the FM detec-
tor, FM stereo MPX decoder, stop level detection, as well as most of the AM circuitry (see
below). U301 further amplifies the IF signal, and then performs FM detection. This detection
uses a double tuned quadrature detector formed by T304 and T305. T305 is adjusted for FM
center frequency by adjusting it for 0VDC between the AFC terminal (U301, pin 4) and the
Vreg terminal (U301, pin 28). T304 is adjusted for minimum distortion (A few iterations may be
required because these two adjustments are dependent on one another). The recovered audio
appears on U301, pin 8.
C313 and its associated components filter the recovered audio and feed it back into U301, pin
9. U301 performs the FM stereo MPX decoding. When you select FM, the decoded L/R chan-
nel signals are sent out on pins 14 and 15. The resistance between pin 12 and ground
controls the separation. 456kHz ceramic resonator CF301 controls the PLL decoder. The PLL
loop filter components are connected to pin 11. Potentiometer R334, which is connected to pin
30, sets the FM stop level to 33dBf (nominal).
C304, R304, C307, and R309 perform FM de-emphasis. Q301, Q302 and their associated
components buffer the signals. MPX filters T301 and T302 remove any unwanted out-of-band
signals before sending them to U101.
The AM loop antenna signal enters the unit through J301’s screw terminals. The signal is then
fed to AM front end module, T303. This device contains an RF tuned section and the AM local