BOSE CD-20 SM Schematic
LIFESTYLE® MODEL 20
MUSIC CENTER
(CD-20)
©
1999 Bose Corporation
Service Manual
Part Number 183884 REV. 02
Last updated 9/20/00
REV01-02 CHANGED MAGAZINE PART NUMBER
Updated page 46 on 02/06/2001
Updated page 46, U2 on 9/19/01
Includes S4, S5, S6, S8, and S9
Contents
Safety Information............................................................................................................................ 2
Electrostatic Discharge Sensitive (ESDS) Device Handling ........................................................ 3
CD-20 Manual Revision Overview ..................................................................................................3
Specifications................................................................................................................................ 4-7
Theory of Operation.................................................................................................................... 8-13
Figure 1. CD-20 Block Diagram ..................................................................................................... 13
Disassembly/Assembly Procedures ....................................................................................... 14-15
Figure 2. Disassembly/Assembly View .......................................................................................... 16
Figure 3. Exploded View of Door ................................................................................................... 17
RC-20 Remote Disassembly/Assembly........................................................................................ 18
Figure 4. RC-20 Disassembly/Assembly View............................................................................... 18
CD Mechanism Disassembly Procedures............................................................................... 19-23
Test Procedures ........................................................................................................................ 24-28
Figure 5. Tuner Alignment Locations.............................................................................................. 28
Remote Control Alignment............................................................................................................ 29
Figure 6. RC-20 Tuning Locations ................................................................................................. 29
Alignment Procedures.............................................................................................................. 30-31
Part List Notes................................................................................................................................ 32
Main Part List.................................................................................................................................. 33
Figure 7. CD-20 Exploded View..................................................................................................... 34
CD Mechanism Part List ................................................................................................................ 35
Figure 8. CD Mechanism Exploded View....................................................................................... 36
Electrical Part List..................................................................................................................... 37-48
Figure 9. RC-20 Remote Exploded View ....................................................................................... 48
RC-20 Remote Part List ................................................................................................................. 49
RC-20 Remote Electrical Part List ........................................................................................... 49-50
Packaging Part List........................................................................................................................ 51
Figure 10. Packaging Exploded View ............................................................................................ 51
Accessory Part List........................................................................................................................ 52
Figure 11. Accessory Packaging ................................................................................................... 52
IC Block Diagrams and Pinouts............................................................................................... 53-55
CD Mechanism IC Block Diagrams.......................................................................................... 56-59
CD Mechanism IC Pin Configuration Tables .......................................................................... 60-66
CD Mechanism IC and Transistor Voltage Tables .................................................................. 67-68
CD Mechanism Troubleshooting.............................................................................................69-86
CD-20 Troubleshooting Waveforms........................................................................................87-91
®
CAUTION: THE BOSE
MODEL 20 (CD-20) MUSIC CENTER CONTAINS NO USER-SERVICEABLE PARTS. TO PREVENT WARRANTY INFRACTIONS, REFER SERVICE TO
WARRANTY SERVICE STATIONS OR FACTORY SERVICE.
1
SAFETY INFORMATION
1. Parts that have special safety characteristics are identified by the symbol on
schematics or by special notes on the parts list. Use only replacement parts that
have critical characteristics recommended by the manufacturer.
2. Make leakage current or resistance measurements to determine that exposed
parts are acceptably insulated from the supply circuit before returning the unit
to the customer. Use the following checks to perform these measurements:
A. Leakage Current Hot Check-With the unit completely reassembled, plug
the AC line cord directly into a 120V AC outlet. (Do not use an isolation
transformer during this test.) Use a leakage current tester or a metering
system that complies with American National Standards Institute (ANSI)
C101.1 “Leakage Current for Appliances” and Underwriters Laboratories
(UL) 1492 (71). With the unit AC switch first in the ON position, then in the
OFF position, measure from a known earth ground (metal water pipe,
conduit, etc.) to all exposed metal parts of the unit (antennas, handle bracket,
metal cabinet, screw heads, metallic overlays, control shafts, etc.), especially
any exposed metal parts that offer an electrical return path to the chassis.
Any current measured must not exceed 0.5 milliamp. Reverse the unit power
cord plug in the outlet and repeat test. ANY MEASUREMENTS NOT WITHIN
THE LIMITS SPECIFIED HEREIN INDICATE A POTENTIAL SHOCK HAZ ARD THAT MUST BE ELIMINATED BEFORE RETURNING THE UNIT TO
THE CUSTOMER.
B. Insulation Resistance Test Cold Check-(1) Unplug the power supply and
connect a jumper wire between the two prongs of the plug. (2) Turn on the
power switch of the unit. (3) Measure the resistance with an ohmmeter be-
tween the jumpered AC plug and each exposed metallic cabinet part on the
unit. When the exposed metallic part has a return path to the chassis, the
reading should be between 1 and 5.2 Megohms. When there is no return path
to the chassis, the reading must be “infinite”. If it is not within the limits specified,
there is the possibility of a shock hazard, and the unit must be repaired and re checked before it is returned to the customer.
PROPRIETARY INFORMATION
THIS DOCUMENT CONTAINS PROPRIETARY INFORMATION OF
BOSE
THE PURPOSE OF SERVICING THE IDENTIFIED BOSE PRODUCT
BY AN AUTHORIZED BOSE SERVICE CENTER OR OWNER OF THE
BOSE PRODUCT, AND SHALL NOT BE REPRODUCED OR USED
FOR ANY OTHER PURPOSE.
®
CORPORATION WHICH IS BEING FURNISHED ONLY FOR
2
ELECTROSTATIC DISCHARGE SENSITIVE (ESDS)
DEVICE HANDLING
This unit contains ESDS devices. We recommend the following precautions when repairing,
replacing, or transporting ESDS devices:
• Perform work at an electrically grounded work station.
• Wear wrist straps that connect to the station or heel straps that connect to conductive floor
mats.
• Avoid touching the leads or contacts of ESDS devices or PC boards even if properly
grounded. Handle boards by the edges only.
• Transport or store ESDS devices in ESD protective bags, bins, or totes. Do not insert unprotected devices into materials such as plastic, polystyrene foam, clear plastic bags, bubble wrap
or plastic trays.
CD-20 MANUAL REVISION OVERVIEW
This service manual contains information about changes to the CD-20 PCB assemblies. It also
includes the original service manual as well as the supplements (183884-S1, 183884-S2,
183884-S3) concerning the CD-20. The following PCB assemblies (as well as the original CD20 PCB) are covered by this service manual. PCB part number 199827 (has a slight change to
the AM circuit to enable the use of a new AM antenna), PCB part number 250736 (incorporates
a new FM section).
3
SPECIFICATIONS
Physical
Dimensions: 2.6"H x 15.5"W x 8"D
(6.6 x 39.4 x 20.3 cm)
Weight: 5.9 lbs. (2.7kg)
Top Cover: Brushed aluminum finish
Bottom Cover: Plastic, Black
Display: Vacuum fluorescent
Power Input: 5mm coaxial power jack Detachable power-pack,
12VAC, 1.6A
Line Level Inputs: Tape, Aux, Video 1, Video 2 RCA Jack pairs
Right=Red, Left=White
Line Level Outputs: Tape RCA Jack pair
Right=Red, Left=White
Zone 1: Miniature 8-pin DIN connector L/R fixed line level audio, L/R
variable line level audio, DC
turn on signal, speaker command data out, audio ground,
and data ground
Zone 2: Miniature 8-pin DIN connector L/R fixed line level audio, L/R
variable line level audio, DC
turn on signal, speaker command data out, audio ground,
and data ground
Serial Data Port: 3.5mm miniature stereo jack data out, data in, and ground
Antenna Input: AM 2.5mm mono jack
FM, 75Ω USA/CSA "F" type
EURO "PAL" type
JAPAN "F" type
Headphone Connector: 3.5mm stereo jack Variable level output
FM Tuner (per IHF-T-200)
Channel Spacing: US: 200 kHz
EURO: 50 kHz
JAPAN: 100 kHz
Band Limits: US: 87.5 MHz-107.9 MHz
EURO: 87.50 MHz- 108.00 MHz
JAPAN: 76.00 MHz-90.00 MHz
De-emphasis: U.S./ Military version: 75µs
EURO version: 50µs
JAPAN version: 50µs
Usable Sensitivity: US: 12 dBf nominal/ 17 dBf limit
EURO: 17 dBf nominal/ 22 dBf limit
JAPAN: 12 dBf nominal/ 17 dBf limit
4
SPECIFICATIONS
)
FM Tuner (per IHF-T-200
(continued)
50 dB Quieting Sensitivity;
Mono: US: 15 dBf nominal/ 20 dBf limit
EURO: 20 dBf nominal/ 25 dBf limit
JAPAN: 20 dBf nominal/ 25 dBf limit
Stereo: US: 37 dBf nominal/ 42 dBf limit
EURO: 42 dBf nominal/ 47 dBf limit
JAPAN: 37 dBf nominal/ 42 dBf limit
Signal to Noise Ratio: Mono: 75 dB nominal/ 70 dB limit
Stereo: 65 dB nominal/ 60 dB limit
Harmonic Distortion: Mono: 0.2% nominal/ 1.0% limit
Stereo: 0.3% nominal/ 1.5% limit
Capture Ratio: 1.5 dB nominal/ 2.5 dB limit
AM Rejection: 60 dB nominal/ 50 dB limit at 45 dBf
Alternate Channel
Selectivity:
Image Rejection: US: 45 dB nominal/ 40 dB limit
RF Inter-modulation: 60 dB nominal/ 50 dB limit
Sub-carrier Product Rejection: 55 dB nominal/ 45 dB limit
Frequency Response: ± 0.5 dB nominal/ ± 1.5 dB limit 30 H z - 15 kHz
Stereo Channel Separation: 40 dB nominal/ 25 dB limit at 1 kHz
US: 70 dB nominal/ 65 dB limit
EURO: 75 dB nominal/ 70 dB limit
JAPAN: 70 dB nominal/ 65 dB limit
EURO: 85 dB nominal/ 70 dB limit
JAPAN: 45 dB nominal/ 40 dB limit
at 65 dBf
US = ± 75 kHz deviation
EURO = ± 40 kHz Deviation
at 65 dBf
at 45 dBf
Auto Stop Level: 32 dBf ± 3 dB
Adjacent Channel Selectivity: 12 dB nominal/ 7 dB limit at 45 dBf
AM Tuner (per IHF-T-100)
Channel Spacing: US: 10 kHz
EURO: 9 kHz
JAPAN: 9 kHz
Band Limits: US: 530 kHz - 1710 kHz
EURO: 522 kHz - 1611 kHz
JAPAN: 522 kHz - 1629 kHz
Usable Sensitivity: 55 dBµV/m nominal/ 60 dBµV/m
limit
Alternate Channel Selectivity: 60 dB nominal/ 50 dB limit
Adjacent Channel Selectivity: 45 dB nominal/ 35 dB limit
Image Rejection Ratio: 40 dB nominal/ 30 dB limit
5
IHF standard test loop
SPECIFICATIONS
)
AM Tuner (per IHF-T-100
(continued)
Signal to Noise Ratio: 50 dB nominal/ 45 dB limit at 100 dBµV/m
Distortion: 1.0% nominal/ 2.0% limit at 100 dBµV/m
Frequency Response: 40 Hz: -3 dB nominal/ -6 dB limit
2 kHz: -3 dB nominal/ -6 dB limit
Auto Stop Level: 60 dBuV/m ± 3 dB
Preamplifier
Input Impedance: AUX/ VIDEO 1, 2 = 33kΩ
TAPE = 48kΩ
Output Impedance: Zone 1, 2 =:220Ω
TAPE: = 220Ω
Output Voltage: FM: 0.6 Vrms
AM: 0.4 Vrms
CD: 2.0 Vrms
Headphone Output: 31 mW ±2 dB 32Ω load, 1 Vrms Aux input
Maximum Output Level: 2.0 Vrms ± 2 dB 1 kHz, THD < .12%
THD: .02% nominal/ .08% limit Output = 1 Vrms
Frequency Response: ± 0.5 dB nominal/ ±1.0 dB limit 20 Hz- 20 kHz
Signal to Noise Ratio: 115 dB nominal/ 100 dB Limit A-weighted, max volume
at 100 dBµV/m, 0 dB
@ 400 Hz
±30%, 1 kHz, max volume
±40%, 1 kHz, max volume
±10%, 1 kHz, max volume
Mono/ 75 kHz dev.
30% mod., 100 dBuV/m
ABEX TCD-782 TNO2
THD <0.15%
Channel Separation: 70 dB nominal/ 50 dB limit
Switching "pops" and "clicks": 1 mV nominal/ 10 mV limit pk, max. vol.
Muting, Zone 1 and 2 outputs: -100 dB nominal/ -90 dB limit
CD Player
Digital to Analog Process: 4X Over-sampling, dual one bit D/A
Maximum Output Level: 2.0 V ± 2 dB
THD + Noise: 0.03% nominal/ 0.12% limit at 1 kHz, 0 dB
Signal to Noise Ratio: 90 dB nominal/ 85 dB limit A-weighted
Channel Separation: 70 dB nominal/ 50 dB limit at 1 kHz
Frequency Response: ± 0.5 dB nominal/ ± 1.0 dB limit 20 Hz - 20 kHz
Low-level Linearity Error: 5.0 dB nominal/ 10.0 dB limit -90 dB
Dynamic Range: 95 dB nominal/ 90 dB limit
6
SPECIFICATIONS
C
D Player
(continued)
Defect Tracking (interruption): 1.0 mm nominal/ 0.8 mm limit ABEX Test Disk TCD-725R
Defect Tracking (black dot): 1.0 mm nominal/ 0.8 mm limit ABEX Test Disk TCD 725R
Defect Tracking (scratch): 1.6 mm nominal/ 1.0 mm limit ABEX Test Disk TCD-721R
Defect Tracking (finger print): 75 µm nominal/ 65 µm limit ABEX Test Disk TCD-725R
Defect Tracking (warped disc): 1.0 mm nominal/ 0.7 mm limit ABEX Test Disk TCD-732RA
Defect Tracking (eccentric disc): 210 µm nominal/ 140 µm limit ABEX Test Disk TCD-714R
Cueing Time: 2 sec nominal/ 3 sec limit Phillips TS4, TNO 1-15
De-emphasis Error: 5 kHz: -4.53 dB ± 2 dB
16 kHz: -9.04 dB ± 2 dB
Disc Access Time: 5 seconds nominal/15 seconds limit Any disc playing to any
other disc playing
Disc Unload Time: 5 seconds nominal/15 seconds limit Any disc playing or stopped
to ejected magazine
7
1.0 Overview
THEORY OF OPERATION
The CD-20 is a self-contained CD player with a 6-disc changer, AM/FM tuner, preamplifier, and
control center for use with Bose
sources (CD and tuner), it allows for up to four external audio sources to be connected (Tape,
Aux, Video 1 and Video 2). It uses an RF remote control, allowing it to be operated from different rooms within a house without the line-of-sight restrictions of an IR remote. No CE-1 type
functionality has been included. All Smart Speaker data commands (i.e.-for AM-25P) have
been implemented.
The CD-20 has two independent output zones, similar to CD-10, accessible through circular
DIN connectors in the back of the product. This allows Zone 1 to play any of the six possible
audio sources, while Zone 2 plays the same source (or any other audio source) simultaneously. The only restriction is that AM and FM cannot be played simultaneously (there is only
one tuner source, usable in only AM or FM mode at a given time).
2.0 Power Supply Electronics (Schematic Diagram Sheet 1)
The unit is powered by an external 12 VAC power supply capable of delivering 1.6 Amps RMS.
D12, D1 and C3 form a positive half-wave rectifier that supplies voltage to the CD_VCC regu-
lator transistor Q10 (which powers the CD mechanism). Feedback components R23, D13 and
R24 sample the CD output voltage, divide it down, and apply it to Q11's emitter. Q11 keeps
Q10 turned on until the CD_VCC voltage reaches the desired level. Once CD_VCC reaches
about 14.5 volts, Q10 goes linear and keeps the output voltage from going any higher. To
disable the CD_VCC supply, the CD_RES line is set to +5V by the microprocessor, which turns
Q1 and Q2 on. Q1 keeps Q11 turned off, while Q2 quickly shorts CD_VCC to ground (turning
the CD mechanism off immediately).
®
powered speaker systems. In addition to the two internal
R2, D4 and C6 form a positive half-wave rectifier that supplies voltage to +5V regulator IC U1.
The +5V circuit powers the microprocessor and EEPROM. The microprocessor monitors the
DETECT line (via comparator U402) in case of a power failure.
D5 and C10 form a positive half-wave rectifier that supplies voltage to +10V regulator IC U2.
The +10V supply powers all the audio circuitry, the tuner, and the enable lines for the external
powered speakers.
C24, R28, R29 and C21 form a resistor/capacitor AC voltage divider that provides the 4.2 VAC
for the VFD (display) filament. The -30 Vdc and -24 Vdc supplies are also for the VFD, and are
generated using a negative voltage tripler. D6, D9, D7, C15, C23, and C18 form the tripler. R11
and zener diode D18 regulate the tripled voltage to -30V. The -24 Vdc supply is divided down
from the -30 Vdc by R26, R12 and R14.
The enable lines (also referred to as +10V control lines) for the powered speakers (Z1_ENBL
and Z2_ENBL) are powered by Q102 and Q104. Q101 and Q103 provide base turn-on current
when the microprocessor sets Z1_ENBL or Z2_ENBL to +5V. The output of the enable lines is
current-limited to less than 100 mA by R134 and R138. This protects against accidental shortcircuits in the speakers or their cables.
8
THEORY OF OPERATION
3.0 Control Electronics (schematic Diagram Sheet 3)
The audio circuits, tuner, CD mechanism, display, EEPROM, remote receiver, push buttons,
and AC power status are all overseen by microprocessor (micro) U400. The micro is clocked
by an 8 MHz ceramic resonator (X401) and is given a reset pulse by U403 (the reset IC). This
occurs whenever the +5V power supply falls below about 4.75V and automatically at power-up.
The micro communicates with all three audio chips (U100, U101, and U102) using a three wire
interface (clock, data and ground). In all three cases, the clock line is the ACLOCK line, port
P35 on the micro. Depending on which chip is being addressed, the micro may use either the
ADATA_1 or ADATA_2 lines to send the data. The data is sent in I2C format to all three chips.
The micro sends commands to the audio chips whenever new input sources are selected, or
the volume needs to change, or a zone needs to mute or unmute.
The micro changes AM and FM tuner stations by writing to the PLL (Phase-Locked Loop) chip
U302. This information is sent using the same clock and data lines used for the audio chips
(ACLOCK and ADATA_2). However, the PLL chip enable (PLL_CE) must also be high for the
chip to receive the message. The micro can tell when a station is strong enough to stop seeking by monitoring the RF_SIG/ line from U300 (the LA1851 detector chip). The micro can then
check to see if that same station is transmitting a valid carrier (in case an adjacent station was
strong enough to fool it into stopping) by asserting the F_TEST line. The result of the frequency test is signaled to the micro by the RF_F_OK line.
The CD-20’s 6-disc CD mechanism is a complete (mechanical as well as electrical) assembly
that is purchased as an OEM unit from FMS (Ford Mazda Sanyo). It comes with its own microprocessor-based controller PCB that is capable of many functions. The CD-20’s micro communicates with this PCB via a dedicated serial data bus (CD_BUS, micro port P12). The CD-20
micro (U400) sends control commands (play, pause, stop, skip forward, etc.) to the mechanism
via the CD_BUS line, and receives disc, track, etc., information in the same way. The CD
mechanism is enabled by U400 by dropping the CD_RES (CD reset) line and raising the
CD_ENBL (CD enable) line. The appropriate control commands are then sent.
The micro controls the vacuum fluorescent display (VFD400) with its on-chip VFD driver. The
driver scans the display’s grids and segments automatically using ports P7, P8 and P9. The
CD-20 display is divided into 8 groups, each enabled by a separate grid line (G1 through G8).
Each of these groups contains up to 15 icons. Each icon is enabled by a separate segment
line (S1 through S15). Although icons appear to be lit constantly, in fact each is actually turning
on and off at a rate too fast to see. Each of the 8 groups of icons are only enabled 1/8th of the
time (first group 1, then group 2, etc., in a repeating sequence). The segment lines are used to
select which icons should be lit as each icon group gets enabled. The 511 Ω series resistors
are added to reduce scan currents that might interfere with AM tuner reception. All series
resistors and inductors on the +5V, +10V, -24V and -30V power supply lines are similarly
added to reduce tuner interference.
U401 is a 1k-bit (128 bytes x 8) EEPROM (Erasable, Programmable Memory) that stores the
AM and FM station presets, RF remote House Code and background (self-test) information.
Whenever a new preset is stored or erased by the user, information gets written to U401. The
micro communicates with the EEPROM using a three wire interface that is identical (but separate) to the interface used for the audio chips. In this case, the clock line is the EE_CLK signal,
port P03, and the data line is the EE_DATA signal, port P04. Although this data is also sent
using the I2C format, the EEPROM is busy enough to have its own interface (rather than
sharing the audio chip’s interface).
9
THEORY OF OPERATION
3.0 Control Electronics (continued)
The micro monitors messages from the RF remote control with input port P30 (RF_DATA). RF
receiver module RR100 demodulates the signals received on the CD-20’s remote antenna (the
digital ground conductor in the audio output cables) and converts it into a low-level AC signal.
This signal is filtered and converted to TTL levels by one-half of comparator U402 before it is
fed to the micro.
Key closures are detected by means of the micro’s on-chip A/D converter. When a console key
is pressed, the voltage divider formed by R419 and R420 is changed by the switch being
pushed. Specifically, a new resistor will be shunted across either R419 or R420. This increases
or decreases the voltage at the micro sense lines, KEY_IN1, KEY_IN2 or KEY_IN3 (note that
the keys are divided into 3 groups of 4 keys each). The micro examines these sense lines and
determines which key is pressed based on the voltage it measures. If the micro measures a
voltage of about 2.5 volts, it knows no key is pressed within that particular group of 4.
The AC power status is monitored by the micro using port P10, pin 1 of U400 (PFAIL/). When
the AC input voltage to the wall transformer falls, its AC output voltage falls below the nominal
12V. When the voltage falls below a certain point (about 88 VAC in FM mode, about 93 VAC in
CD mode), the DETECT line from the power supply (which monitors the raw DC input voltage
to the +5V regulator, U1) causes comparator U402’s output to go low. This warns the micro
that the power is failing, and it responds by shutting the system down (muting the speaker
outputs, blanking the display, etc.). When AC power is OK, U402’s output (PFAIL/) is high.
4.0 Audio Electronics (Schematic Diagram Sheet 2)
The CD-20 has 2 internal audio sources (CD and tuner) and four external sources (Tape, Aux,
Video 1 and Video 2). All of the sources get routed through audio matrix chip U101. This IC
controls which zone(s) the sources will be connected to. The chip has three left and right
outputs. One is used for Zone 1, two for Zone 2, and three for the tape outputs. The micro
instructs the chip to connect each of the outputs to the correct input by using the clock and
data lines as described above. If a zone is not active (or muted), the audio matrix chip may
connect that output to an internal reference rather than one of the inputs for extra muting. The
matrix has internal buffer amps, allowing its outputs to be used directly as the Zone 1 and
Zone 2 fixed audio outputs.
Output #3 from U101 (pins 16 and 17) is used for the CD-20’s left and right Tape output. The
micro sees to it that this output nominally is connected to the same input source as the Zone 1
output. This means that any tape deck connected to the Tape outputs would record the same
source that is being played on Zone 1. However, if the Tape input is selected for Zone 1, the
Tape outputs are muted by the micro to prevent a feedback loop.
The first two matrix chip outputs (pins 12 through 15), as described, are then fed to Zone 1 and
Zone 2 volume control ICs (U100 and U102 respectively). Each IC contains the volume-control
cell, output-buffer cell and output mute cell for that particular zone. Volume settings, mute
settings and output-buffer switching are all controlled by the micro using the ACLOCK,
ADATA_1 (for Zone1) and ADATA_2 (for Zone2) lines. The final LR audio outputs (called the
“adjustable outputs,” after volume control and muting) are pins 24 and 25. From here, the
audio passes through DC blocking capacitors C114, C214, C124 and C224 (the volume control
ICs run on a single +10V supply, so the audio has a 5 Vdc offset component) before running to
output circular DIN connectors J101A and J101B.
10
THEORY OF OPERATION
4.0 Audio Electronics (continued)
Each of the volume control chips has two independently mutable outputs. The #1 outputs are
used for the speakers (as described above). The #2 output of the Zone 1 volume chip is used
for CD-20’s Headphone output (the #2 output on the Zone 2 chip is not used). Anyone plugging
in headphones would therefore hear the same source that was previously being played by the
Zone 1 speakers. The microprocessor monitors the HP_SENSE line from the headphone jack
to tell if headphones are plugged in. When they are, the micro mutes the #1 outputs from the
Zone 1 volume chip (to the speakers), and unmutes the #2 outputs (to the headphones). The
opposite occurs when headphones are unplugged. The headphone signals are buffered by
U104 in order to drive the required 32 Ω loads.
Audio from the CD player typically contains a great deal of motor noise. This noise occurs
because of ground conductor voltage drops on the ribbon cable connecting to the mechanism.
To eliminate this motor noise, op-amp U103 has been configured as a differential amplifier. Any
motor noise signals on the left and right audio lines are also on the ground reference line, pin 2
of the CD ribbon cable (pin 2 of connector J110). Therefore, U103 eliminates this commonmode component without affecting the actual audio (which is purely a differential-mode component). At the same time, U103 provides the necessary gain for the CD signal.
5.0 Tuner Electronics (Schematic Diagram Sheet 4)
The FM antenna signal comes in through F connector J301 and enters the FM front-end
module (U301). U301 contains a tuned RF amplifier, the FM local oscillator, and the first mixer.
The 10.7 MHz IF output signal appears on pin 4 and is passed through a 10.7 MHz ceramic
filter (CF300). The filter's output is amplified by the first IF gain stage. This stage consists of
Q307, Q308 and their associated components. The signal is then passed through a second
ceramic filter (CF301), a second gain stage (Q309, Q310, etc.) and a third ceramic filter
(CF302). These filter stages reject unwanted FM stations and noise.
The output of the final ceramic filter is fed into the main detector IC (U300). This device contains a second mixer, the FM detector, FM stereo MPX decoder, stop-level detection, as well
as most of the AM circuitry. U300 further amplifies the IF signal and then performs FM detection using a double tuned quadrature detector formed by T303 and T304. T304 is adjusted for
FM center frequency by adjusting it for 0 VDC between the AFC terminal (pin 4, U300) and the
VREG terminal (pin 28, U300). T303 is adjusted for minimum distortion. (These two adjustments are interactive, so a few repetitions may be required.) The recovered audio appears on
pin 8 of U300.
The recovered audio is filtered by C326 and the associated components and fed back into
U300 on pin 9. U300 performs the FM stereo MPX decoding and outputs the decoded L and R
channels (when FM is selected) on pins 14 and 15. The separation is controlled by the resistance from pin 12 to ground. The PLL decoder is clocked by 456 kHz resonator X300. The PLL
loop filter components are connected to pin 11. The FM stop level is set by the variable resistance R349 on pin 30 and is nominally set to 33 dBf.
The signals are buffered and amplified by op-amp U303 and its associated components.
Components R301, C302, R305, and C303 perform FM de-emphasis. MPX filters T301 and
T300 remove any unwanted out-of-band signals.
11
THEORY OF OPERATION
5.0 Tuner Electronics (continued)
The signal from the AM loop antenna enters the unit through the 2.5 mm AM jack (J300) and is
fed to the AM front end module (T302). This device contains an RF tuned section and the AM
local oscillator tuner circuit. The tuned output appears on pin 12 and is fed to the AM buffer
FET transistor Q303. The buffered output is sent to pin 27 of U300 which contains the AM RF
amplifier, mixer, IF amplifier, AM detector, and AM stop level detection. The AM stop level is set
by the variable resistor R348 on pin 16 and is nominally set at 70 dBuV/m. The AM IF output
signal appears on pin 26. This signal is filtered by the IF filter T306 and fed back into the chip
on pin 24 for AM detection. The AM detected output appears on pin 5 where it is filtered by
C327, R328 and C328. The filtered output is fed back into U300 on pin 6 where it is sent to the
L and R outputs (when AM is selected), pins 14 and 15.
The AM and FM local oscillators are controlled by the PLL IC (U302). This device is instructed
by the micro to select either AM or FM and to tune to a particular frequency. The PLL reference
oscillator is clocked by a 7.2 MHz crystal (X301). This frequency is divided down to 400 kHz
and then appears on pin 7. U302 divides down the Local Oscillator (LO) frequency and compares it to an internal reference frequency. An error signal from the comparison appears on pin
18. This error signal is integrated and filtered by Q304, Q305, and associated components.
This produces the tuning voltage which appears at the collector of Q304.
The tuning voltage is filtered by R312, C316, R311, and C309 and fed to pin 14 of the AM front
end (T302). Here it is used to vary the capacitance of 2 varactor diodes. The first diode adjusts
the frequency of the AM local oscillator. The second tunes the AM RF input section to the
desired frequency. Similarly, in FM mode, the tuning voltage is filtered by R316 and C321 and
fed to the FM front end. As in the AM case, the FM front end uses this voltage to vary the LO
frequency and to tune the RF input sections.
12
THEORY OF OPERATION
Figure 1. CD-20 Block Diagram
13
DISASSEMBLY/ASSEMBLY PROCEDURES
Note: Refer to Figures 2 and 3 for the
following procedures. Numbers in parentheses correspond to the item callouts in
Figures 2 and 3.
1. Top Cover Removal
1.1 Grasp the cover (1) by the edges and
work it up to release the christmas tree
fasteners from the superstructure (2).
This might take some effort. Using a flatblade screwdriver may be helpful. Take
care not to damage the top cover.
2. Top Cover Replacement
2.1 Align the cover's christmas tree fasten-
ers with the holes in the superstructure (2).
Push the cover (1) down until it is fully
seated.
Note: Align the cover so that the BOSE
logo is in the left corner.
3. Display Window Removal
3.1 Grasp the top edge of the display
window (3) and pull it forward.
4. Display Window Replacement
5.4 Remove the three screws (4) from the
superstructure.
5.5 Place a flat-blade screwdriver into each
of the four slots (5) on the superstructure
and push away from the center of the unit
to release the catches.
5.6 Lift the superstructure away from the
base (9).
6. Superstructure Replacement
6.1 Lower the superstructure (2) onto the
base (9) and pull the ribbon cable through
the large opening.
6.2 Push down on the superstructure
(2) until it snaps into the base (9).
®
6.3 Redress the ribbon cable in the
channel at the rear of the superstructure
(2). Connect the cable to the PCB.
6.4 Replace the three screws (4) that
secure the superstructure to the base.
6.5 Replace the door spring (7) to the
superstructure and door assembly (8).
4.1 Align the display window (3) so the
catches are facing up.
4.2 Align the display window with the LCD
and press it into the superstructure (2).
5. Superstructure Removal
5.1 Perform procedures 1 and 3.
5.2 Remove the door spring (7) from the
superstructure (2) and door assembly (8).
5.3 Remove the ribbon cable (6) from the
super structure and disconnect it from the
PCB (18).
Note: Make a note of how the ribbon cable
was dressed in the rear channel of the
superstructure.
6.6 Perform procedures 2 and 4.
7. Door Assembly Removal
Note: Refer to Figure 3 for the following
procedures.
7.1 Perform procedure 5.
7.2 Lift the door assembly (8) straight up.
8. Door Assembly Replacement
8.1 Lower the door assembly (8) into the
base (9) aligning the post (10) on the door
assembly to the holes (11) in the base.
Also rotate the hinge (12) on the left side of
the door so that the groove fits into the slot
on the hinge holder (13).
8.2 Perform procedure 6.
14
DISASSEMBLY/ASSEMBLY PROCEDURES
9. CD Mechanism Removal
9.1 Perform procedure 5.
9.2 Lift the CD mechanism (14) straight up
from the base (9).
10. CD Mechanism Replacement
10.1 With the opening of the CD mecha-
nism facing towards the front of the unit,
lower the CD mechanism into the base (9)
aligning the four grommets (15) with the
four posts on the base (two not shown).
Note: Make sure the four springs (16) are
located on the four outer posts of the base.
10.2 Perform procedure 6.
11. Control Panel Removal
11.1 Perform procedure 5.
14. PCB Assembly (Disassemble)
14.1 The power supply PCB (21) and the
tuner PCB (22) are plugged into the main
PCB (23). Grasp the power supply PCB or
the tuner PCB and pull in an outward
direction from the main PCB.
15. PCB Assembly (Assemble)
15.1 Connect the power supply (21) and
the tuner PCB (22) to the main PCB by
plugging them into the main PCB (23) via
connectors: J3 and J4 on the power
supply PCB, J306 and 307 on the tuner
PCB. Tabs on the tuner and power supply
PCB lock into slots on the display PCB
(24) to create a mechanical support.
16. PCB Assembly Replacement
11.2 Grasp the top edge of the control
panel (17) and pull it forward.
12. Control Panel Replacement
12 1 Tilt the control panel (17) forward and
place it into the base (9) so that the lower
edge of the control panel is in front of the
catches on the base. Tilt the control panel
towards the rear of the base until the
control panel snaps into place.
13. PCB Assembly Removal
13.1 Perform procedure 5.
13.2 Grasp the PCB assembly (18) and lift
it straight up.
13.3 The RCA jack PCB (19) and the
headphone PCB (20) are wired to the PCB
assembly. Lift the RCA Jack PCB and the
headphone PCB straight up.
16.1 While lowering the PCB assembly
(18) into the base (9), angle it so that the
RCA jacks protrude out the rear of the
base.
16.2 Insert the RCA Jack PCB (19) into
the holes in the base marked “TAPE IN,
TAPE OUT”. The superstructure (2) will
give mechanical support to the RCA
Jacks.
16.3 Insert the headphone PCB (20)
with connector J612 up, into the slot.
16.4 Redress all wires.
Note: When removing the PCB, make a
note of the wire dressing for reinstallation.
15
Figure 2. Disassembly/Assembly View
16
HINGE
12
8
12
10
9
11
Figure 3. Exploded View of Door
17
13
FRONT VIEW
HINGE HOLDER
RC-20 REMOTE DISASSEMBLY/ASSEMBLY
Note: Numbers in parentheses correspond
to the callouts in Figure 4.
1. Enclosure Disassembly
1.1 Slide off the battery compartment door
(5) and remove the batteries.
1.2 While holding the top cover (4) with one
hand, place your fingers from your other
hand in the battery compartment and grasp
the lower part of the bottom cover (3) with
your finger tips.
1.3 With your finger tips in the battery
compartment, first pull parallel to the unit
then pull perpendicular.
1.4 With the catches released at the bottom, work your fingers up the sides to
release the rest of the catches.
2. Enclosure Assembly
2.1 Lower the bottom cover (3) onto the top
cover (4) so that the bottom cover's lip fits
over the top cover.
2.2 Press the top cover and bottom cover
together until they snap into place.
3. PCB Removal
3.1 Lift the PCB (1) straight up. The
springs will come up with the PCB.
4. PCB Replacement
4.1 Lower the PCB (1) into the bottom
cover (3) so that the springs are in the
battery compartment.
5. Pad Removal
5.1 The pad (2) is not secured. Grasp a
corner of the pad and lift it out.
6. Pad Replacement
6.1 Lower the pad (2) into the top cover
(4) so that the buttons line up with the
holes in the top cover.
5
6
7
8
CATCHES
3
10
1
2
9
CATCHES
4
11
Figure 4. RC-20 Disassembly/Assembly View
18
CD MECHANISM DISASSEMBLY PROCEDURES
1. Main PCB Disassembly
1.1 Short the two pads on the ribbon cable
coming from the pick up.
1.2 Unplug CN905.
1.3 Remove the four screws that secure the
PCB to the chassis.
1.4 Lift the PCB up and remove the remaining connectors.
2. Base Chassis Disassembly
2.1 Remove all the FPCs that connect the
mount chassis (A173) to the main PCB.
2.2 Remove the front and rear elevator
tension spring (A59).
2.3 Remove the two E-rings located in the
rear (A238) and the two located in the front
(A241). Remove the two E-rings located in
the front (A235) and the two located in the
rear (A236). Remove the link cross bars
(A107) and (A111).
2.4 Remove the screw (A133) and the two
screws (A131) that mount the elevator unit
and remove the elevator unit.
Note: A133 is the screw that secures the
plastic piece.
2.5 Remove the six screws (A61) that
secure the top base chassis (A14).
2.6 Remove the two screws (A63) and the
two screws (A64) that secures the rear
base chassis (A22). Remove the spring
that connects from the mount chassis to the
base chassis.
Note: Use caution when removing the
mount chassis so that the washers, rollers,
etc. that are mounted on the lift pin of the
mount chassis are not lost.
(Continued on the next page)
19
CD MECHANISM DISASSEMBLY PROCEDURES
Note: When installing the mount chassis
(A173), line up the elevator shaft (A119) so
that the lever (A55) is almost touching the
eject lever (A45). The mount chassis
should be at it's lowest position.
3. Elevator Motor Disassembly
3.1 Unplug the FPC (A104) from the PCB.
3.2 Remove the screw (A133) that secures
the elevator unit.
Note: A133 is the screw that secures the
plastic piece.
3.3 Remove the two screws (A131) that
secure the elevator unit to the base chassis
and remove the elevator unit. Lift the
elevator unit out through the bottom of the
base chassis.
3.4 Remove the FPC (A104) from the
motor (A127) terminal with a soldering iron.
3.5 Remove the screw (A130) that secures
the elevator motor bracket (A115) to the
elevator unit bracket.
3.6 Remove the two screws (A132) that
secure the motor to the motor bracket.
20
CD MECHANISM DISASSEMBLY PROCEDURES
4. Feed Motor Disassembly
4.1 Remove the washer (A102) and then
remove the DV middle gear (A81).
4.2 Remove the FPC from the feed motor
with a soldering iron.
4.3 Remove the two screws (A94) that
secure the feed motor (A89). Lift the motor
up.
5. Loading Motor Disassembly
5.1 Unplug the FPCs (A104) and (A232).
5.2 Remove the four screws (A64) that
secure the base chassis side (A19) to the
base chassis.
5.3 Remove the screw (A133) that secures
the elevator unit to the chassis. Remove
the base chassis side (A19). The elevator
unit will be attached to the base chassis
side.
5.4 Remove the two screws (A246) that
secure the loading motor unit to the base
chassis.
5.5 Remove the FPC (A232) that is connected to the motor terminal with a soldering iron.
5.6 Remove the two screws (A242) that
secure the motor (A233) to the motor
mount.
Note: Assemble in the reverse order of the
disassembly and make note of the following.
1. Make sure the front bend of the friction
gear arm assembly (A197) is inserted in
the square hole of the chassis mount
(A173).
2. Make sure that the PR cam roller (A223)
is fitted to the push cam rod (A215) and is
inserted in the bend groove of the push rod
(A221).
3. The tightening torque of the motor
mounting screw (A242) is 1.5 to 2.0 kg-cm.
21
CD MECHANISM DISASSEMBLY PROCEDURES
6. Lift Motor Disassembly
6.1 Perform procedure 3.
6.2 Remove the two DL springs (A228) that
are located on both sides. The DL springs
are black.
6.3 Remove the FPC from the lift motor
(A154) with a soldering iron.
6.4 Grasp the unit where the DL springs
were located and rotate the motor assembly section up. Remove the two screws
(A157) that secure the motor bracket to the
assembly.
Note: Rotate the worm gear A148 until the
disc rollers are in contact.
6.5 Remove the E-ring (A156) and the
washer (A166) that secures the worm gear
to the motor shaft.
6.6 Remove the screw (A158) that secures
the motor to the motor bracket.
7. Pick Up Disassembly
7.1 Short the short pattern located on the
FPC (A1) with a soldering iron. Unplug the
FPC (A1).
7.2 Remove the screw (A101) that secures
the FPC to the chassis. Make note of the
location of the FPC that is glued to the
chassis.
7.3 Remove the two screws (A96) that
secure the screw clip (A78), DV plate
spring (A86) and DV spring holder (A76) to
the pick up (A87).
7.4 Remove the screw (A97) that secures
the switch spacer to the chassis.
7.5 Remove the two screws (A93) that
secure the sub shaft (A73) of the pick up to
the chassis. Lift the pick up out of the unit.
22
CD MECHANISM DISASSEMBLY PROCEDURES
Note: When replacing the pickup, grease
the main shaft and the U groove of the sub
shaft. After securing the FPC, apply glue to
the end opposite the screw.
8. Manual Magazine Ejection
8.1 With the disc clamped, rotate the lift
motor worm gear (A148) 25 to 28 turns in
the direction of the arrow to unclamp the
disc.
8.2 With the disc unclamped, rotate the L
wheel worm gear (A212) in the direction of
the arrow to return the disc to the magazine.
Note: If the disc comes in contact with the
separator and can not be returned, push
the edge of the disc up or down so that it
returns without coming into contact with the
separator of the magazine.
8.3 After returning the disc to the magazine,
push the emergency eject plate (A51) with
the tip of a screwdriver to remove the
magazine.
23
TEST PROCEDURES
General Test Setup
Use cable 184209 for fixed level tests.
Use cable 183174 for adjustable level tests.
The miniature switch number 8 on the
remote must be up to control ZONE 2.
For ZONE 1 and 2 variable tests, adjust the
volume to max.
Terminate the Headphone output into 32Ω.
Terminate all Audio outputs into 10KΩ.
Terminate the serial output jack (tip and
ring) into 10kΩ (two resistors).
See Figure 5 for adjustment locations.
1. Aux Gain and Separation Test
1.1 Apply a 2 Vrms, 1 kHz signal to the left
AUX input.
1.2 Ground the TAPE, VIDEO 1, VIDEO 2
and right AUX inputs.
1.3 Reference a dB meter to the applied
signal.
1.4 Measure the gain according to the
chart below.
Note: Repeat this test for the right channel.
OUTPUT MIN dB MAX dB
Zone 1 L Fixed -1.5 1.0
Zone 1 L Adjustable -1.5 1.0
Zone 2 L Fixed -1.5 1.0
Zone 2 L Adjustable -1.5 1.0
Tape L -1.5 1.0
Headphone L -- -50
Zone 1 R Fixed -- -50
Zone 1 R Adjustable -- -50
Zone 2 R Fixed -- -50
Zone 2 R Adjustable -- -50
Tape R -- -50
Headphone R -- -50
2. Video Gain And Separation Test
2.1 Apply a 2 Vrms, 1 kHz signal to the left
VIDEO 1 input.
2.2 Ground the TAPE, VIDEO 2, AUX and
right VIDEO 1 inputs.
2.3 Reference a dB meter to the applied
signal.
2.4 Measure the gain according to the
following chart.
Note: Repeat this test for the right channel
and VIDEO 2.
OUTPUT MIN DB MAX
DB
Zone 1 L Fixed -1.5 1.0
Zone 1 R Fixed -- -50
Zone 2 L Fixed -1.5 1.0
Zone 2 R Fixed -- -50
Tape L -- -50
3. Tape Gain and Separation Test
3.1 Apply a 2 Vrms, 1 kHz signal to the left
TAPE input.
3.2 Ground the VIDEO 1, VIDEO 2, AUX
and right TAPE inputs.
3.3 Reference a dB meter to the applied
signal.
3.4 Measure the gain according to the
chart below.
Note: Repeat this test for the right channel.
OUTPUT MIN dB MAX dB
Zone 1 L Fixed -1.5 1.0
Zone 2 L Fixed -1.5 1.0
Zone 1 R Fixed -- -50
Zone 2 R Fixed -- -50
24
TEST PROCEDURES
4. Volume Control Mute Test
4.1 Apply a 2 Vrms, 1 kHz signal to the
AUX input.
4.2 Set the volume control to maximum.
4.3 Reference a dB meter to ZONE 1
adjustable output.
4.4 Set the volume control to minimum and
measure ZONE 1 output (should be ≤ -80
dB).
5. Distortion Test
5.1 Apply a 1 Vrms, 1 kHz signal to the
AUX input (Volume at full).
5.2 Measure the distortion at ZONE 1 and
ZONE 2 (should be ≤ .05% A-weighting).
6. Frequency Response Test
6.1 Apply a 1 Vrms, 20Hz signal to the AUX
input (Volume at full).
6.2 Reference a dB meter to the applied
signal.
7.3 While adjusting the volume up or down,
the voltage at the tip should be ≥ .6 VDC.
8. FM Alignment
8.1 Select FM and tune to 98.1 MHz. Inject
an RF signal into the FM antenna terminals at 40 dBf, mono modulation, pilot off.
8.2 Front End Mixer Coil Adjustment:
Connect a DC meter to U300, pin 25.
Adjust the FM front end mixer coil for
maximum DC voltage (should be within
+0, -20 mV of peak value).
Note: The front end mixer coil is located in
the front end module (it is the only adjustable coil).
Note: Do not perform the following test for
PCB 250736.
8.3 FM Detector Zero adjustment:
Connect a DC meter to the positive (+)
side of C315 and the positive (+) side of
C313. Adjust T304 for 0 Vdc ± 110mV.
8.4 FM Distortion adjustment:
Adjust T303 for minimum distortion
(viewed at tape output).
6.3 Measure ZONE 1 and ZONE 2 output
(should be ± 1 dB).
6.4 Apply a 1 Vrms, 20 kHz signal to the
AUX input.
6.5 Reference a dB meter to the applied
signal.
6.6 Measure ZONE 1 and ZONE 2 output
(should be ± 1 dB).
7. Serial Data Interface Port
7.1 The voltage at the ring of the serial data
jack should be ≥ 4.5 VDC.
7.2 The voltage at the tip of the serial data
jack should be ≤ 0.8 VDC.
8.5 FM distortion should be < .6%. If the
distortion is out of spec, repeat 8.3 and
8.4. Recheck FM distortion.
9. FM Stereo Separation
9.1 Inject an RF signal into the FM antenna terminal at 65 dBf, L only modulation, pilot on.
9.2 Connect a dB meter to the left TAPE
output. Reference the dB meter to this
point.
9.3 Connect the dB meter to the right
TAPE output. The output should be ≤ -25
dB.
25
TEST PROCEDURES
10. FM Stop Level Adjustment
Note: Do not perform the following test for
PCB 250736.
10.1 Inject an RF signal into the FM antenna ternimals at 25 dBf, L+R modulation,
pilot off, set to 98.1 MHz.
10.2 Connect a DC meter to pin 21 of
U300.
10.3 Rotate R439 counterclockwise until
the voltage becomes less than 2.5V, then
clockwise until the voltage becomes greater
than 2.5V. The correct adjustment is when
the voltage just becomes sightly greater
than 2.5V.
10.4 Increase the RF generator to dBf and
confirm that the voltage at pin 21 U300 is
less than 2.5V.
11. FM Sensitivity / SNR
12.4 Tune the generator and the unit to
1080 kHz. Adjust the brown slug of T302
for maximum output.
12.5 Repeat steps 12.3 and 12.4 until
maximum output is obtained.
13. AM Sensitivity
13.1 Inject an RF signal, 1080 kHz, at a
field strength of 70 dBu to the AM antenna
terminals.
13.2 Connect a dB meter to the TAPE
output and reference it to this point.
13.3 Remove the RF signal and measure
the TAPE output (should be ≤ - 30 dB).
14. AM Stop Level adjustment
14.1 Inject an RF signal at a field strength
of 59 dBu to the AM antenna terminal.
11.1 Inject an RF signal into the FM antenna terminals at 42 dBf, L=R modulation,
pilot on.
11.2 Connect a dB meter to the TAPE
output. Reference the dB meter to this
point.
11.3 Turn the modulation off and measure
the output. The output should be ≤ -50 dB
for US versions and ≤ -45 dB for European
versions.
12. AM RMS
12.1 Inject an RF signal at a field strength
of 70 dBu into the AM antenna terminals.
12.2 Connect an AC meter to the tape
output.
12.3 T une the generator and the unit t
630 kHz. Adjust the black slug of T302 for
maximum output. The output should be
≥ 300 mVrms.
14.2 Connect a DC meter to pin 21 of
U300.
14.3 Rotate R348 counterclockwise until
the voltage becomes less than 2.5V, then
clockwise until the voltage becomes greater
than 2.5V. The correct adjustment is when
the voltage just becomes slightly greater
than 2.5 VDC.
14.4 Increase the generator output to 64
dBu and confirm the voltage at pin 21 of
U300 is less than 2.5V.
26
TEST PROCEDURES
15. CD Tracking Ability
15.1 The test discs listed in the chart below
should be played with no audible defects.
15.2 If the unit fails any of these tests,
replace the CD mechanism assembly or
proceed to the Alignment procedures.
Disc Test Test Conditions
ABEX test disc TCD-725A Defect tracking (void), 1.0 mm Track 6, 6 sec.
ABEX test disc TCD-725A Defect tracking (black dot), .8 mm Track 9, 8 sec.
ABEX test disc TCD-725A Defect tracking (finger print), 65 µm Track 13, 10 sec.
ABEX test disc TCD-732R Defect tracking (warped disc), -1.0 mm First and last track, 6 sec.
ABEX test disc TCD-713R Defect tracking (eccentric disc), 210 µm First and last track, 6 sec.
27
TEST PROCEDURES
PCB 178335
PCB 199827
PCB 250736
Figure 5. Tuner Alignment Locations
28
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