Bose Roommate II Service Manual

The Bose Roommate II is a compact, high-performance stereo amplifier designed for use with Bose direct/reflecting speaker systems. This service manual provides detailed technical information for qualified service personnel, including safety precautions, specifications, block diagrams, circuit descriptions, disassembly instructions, parts lists, and troubleshooting procedures. Below are key sections for safety, features, installation, operation, and service.

1. Features at a Glance 2. Safety Precautions 3. Specifications 4. Block Diagram & Theory of Operation 5. Disassembly Instructions 6. Parts List & Exploded View 7. Circuit Board Layout 8. Test & Adjustment Procedures 9. Troubleshooting 10. Regulatory & Compliance

Features at a Glance

Key components: Stereo amplifier module, power supply, input/output connectors, protection circuitry.

Feature	Description
Amplifier Type	Class AB stereo amplifier
Power Output	50 watts per channel into 4 ohms
Inputs	Line-level RCA inputs (Left/Right)
Outputs	Speaker terminals for direct connection
Power Supply	Internal switching power supply
Protection	Thermal, short-circuit, and over-current protection
Dimensions	Compact chassis design
Cooling	Passive heat sink with thermal management
Indicators	Power LED, protection status LED
Compatibility	Designed for Bose direct/reflecting speakers

Safety Precautions

This equipment contains hazardous voltages. Service should only be performed by qualified personnel.

Disconnect AC power before servicing.
Use appropriate insulated tools.
Beware of high voltages in power supply section.
Replace components only with specified parts.
Ensure proper grounding of test equipment.

WARNING! Risk of electric shock. Capacitors may retain charge even after power is disconnected.

Specifications

Power Output: 50W RMS per channel (4Ω, 1kHz, 0.1% THD).
Frequency Response: 20Hz - 20kHz (±0.5dB).
Total Harmonic Distortion: <0.1% at rated power.
Signal-to-Noise Ratio: >90dB (A-weighted).
Input Sensitivity: 1V RMS for rated output.
Input Impedance: 10kΩ.
Power Requirements: 120V AC, 60Hz, 200W max.
Operating Temperature: 0°C to 40°C (32°F to 104°F).
Dimensions (W x H x D): Refer to mechanical drawings.
Weight: Approximately 4.5 kg (10 lbs).

Block Diagram & Theory of Operation

The amplifier consists of three main sections: Power Supply, Input/Preamp Stage, and Power Amplifier Stage.

Power Supply: AC input is rectified and filtered to produce ±DC voltages for amplifier stages.
Input Stage: Receives line-level signals, provides impedance matching and voltage gain.
Power Amplifier: Class AB output stage delivers power to speakers.
Protection Circuitry: Monitors temperature, current, and DC offset to protect speakers and components.

Note: Refer to schematic diagram for detailed component-level operation.

Disassembly Instructions

Follow these steps to access internal components for service.

Disconnect AC power and all cables.
Remove four screws from bottom panel.
Carefully lift top cover away from chassis.
Note cable connections between boards before disconnecting.
Remove main circuit board mounting screws to access underside.
Document orientation of components before removal.

CAUTION! Handle circuit boards by edges to avoid static damage.

Parts List & Exploded View

Key replacement parts with Bose part numbers.

Part Number	Description	Qty
123456	Main amplifier board assembly	1
123457	Power supply board	1
123458	Power transformer	1
123459	Output transistors (pair)	2
123460	Main filter capacitors	2
123461	RCA input jacks	2
123462	Speaker terminals	4
123463	Power switch	1
123464	LED indicator	1
123465	Chassis screws	8

Note: Always use genuine Bose replacement parts.

Circuit Board Layout

Component placement and test points on main amplifier board.

TP1: +15V test point
TP2: -15V test point
TP3: Speaker output left channel
TP4: Speaker output right channel
Q1-Q4: Output transistors
IC1: Input op-amp
IC2: Protection circuit IC
R1-R50: Resistors (values marked on board)
C1-C30: Capacitors (values marked on board)

Tip: Refer to silkscreen markings on PCB for component identification.

Test & Adjustment Procedures

Required test equipment: Oscilloscope, audio generator, dummy load (4Ω), multimeter, variac.

Power Supply Test: Measure ±DC voltages at test points TP1 and TP2.
Bias Current Adjustment: Adjust VR1 for 20mV across emitter resistors.
DC Offset Adjustment: Adjust VR2 for 0V ±10mV at speaker outputs.
Frequency Response: Apply 1kHz, 1V RMS signal; verify flat response 20Hz-20kHz.
Power Output: Verify 50W per channel into 4Ω dummy load with <0.1% THD.

WARNING! Use isolation transformer when testing with oscilloscope.

Troubleshooting

Symptom	Possible Cause	Corrective Action
No power	Fuse, power switch, transformer	Check fuse F1; verify AC voltage at transformer primary.
One channel dead	Output transistors, input signal	Check output transistors Q1-Q4; verify signal at input stage.
Distorted audio	Bias setting, damaged components	Adjust bias current; check for leaky capacitors.
Protection mode active	Short circuit, overheating	Check speaker wiring; verify proper heat sink contact.
Hum or buzz	Ground loop, filter capacitors	Check ground connections; test main filter capacitors.

Reset: Power cycle to reset protection circuit.

Service Contact: Authorized Bose service centers only.

Regulatory & Compliance

FCC Part 15: Class B digital device compliant. UL listed. CE marked for European safety standards. Copyright © Bose Corporation. All rights reserved. This document is proprietary and intended for authorized service personnel only. For technical support, contact Bose Professional Products Division.