BOSE 318882-B2 NOISE FLOOR BULL Schematic
SERVICE BULLETIN
Bulletin Part Number: 318882-B2
Product: L1 Compact Portable Line Array System
Subject: Excessive noise floor on the Channel 1 mic input
Disposition: On all L1 Compact systems built before 8/18/09 (DOM 9230) that are sent in for repair due to
excessive noise floor on the channel 1 mic input, replace the six resistors listed in step 2 of the below rework
procedure. Also replace two resistors in the channel 2 circuitry to improve the long-term performance of the
channel 2 volume control potentiomenter.
Symptom: Excessive noise floor on the Channel 1 mic input.
Reason: Circuit gain initially set too high during design.
Solution: Perform the rework procedure below.
Rework Procedure:
CAUTION! The integrated circuits used on the Input / Output PCB are extremely sensitive to damage from
electrostatic discharge. Observe all ESD handling procedures to prevent damage to the PCB assembly during
the rework process.
1. Using the disassembly procedures in the service manual, remove the handle from the power stand.
Remove the top cover with the Input / Output PCB mounted to it. It is not necessary to remove the I/O board
from the top cover plastic to perform this rework procedure.
2. Locate the following SMD resistors and replace them with the values listed below. Refer to the board layout
diagram on page 2 of this bulletin for the resistor locations. All resistors are SMT package size 0603, 1% parts.
Mic (channel 1) Noise Reduction:
Change R117 to 47.5 Ohm - Bose part number 191465-47R5
Change R171 to 4.7K - Bose part number 191465-4701 (position was unused previously)
Change R165 to 68.1K - Bose part number 191465-6812
Change R31 1 to 24.9K - Bose part number 191465-2492
Change R248 to 13.7K - Bose part number 191465-1372
Change R190 to 10K - Bose part number 191465-1002
Lower Wiper Resistor Value for Channel 2:
Change R1 18 to 68.1K - Bose p art number 191465-6812
Change R1 19 to 68.1K - Bose p art number 191465-6812
3. Re-install the I/O PCB assembly and the handle into the power stand cabinet.
4. Perform the power stand test procedures located in the L1 Compact service manual to ensure proper
operation before returning the system to the customer.
Note: Refer to the L1 Compact service manual, 318882-SM, located on the service web site located at
http://serviceops.bose.com for disassembly and test procedures.
Date Issued: 8/09
Bose Corporation; The Mountain, Framingham, Ma. 01701-9168
Service documentation available online at http://serviceops.bose.com
page 1 of 2
SERVICE BULLETIN
R118
R119
R311
R248
R117 R171
Input / Output PCB Component Locations for Rework Procedure
Bose Corporation; The Mountain, Framingham, Ma. 01701-9168
Service documentation available online at http://serviceops.bose.com
R165
R190
page 2 of 2
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