Bose FreeSpace 4400 Service Manual page 61

DISASSEMBLY PROCEDURES
4.3 Remove the four nuts, lock washers and
flat washers (19, 20, 21) that secure the fan
(22) to the chassis (1). Lift out the fan.
Re-assembly Note: Be sure to re-install the
fan facing the correct direction. Air should
flow into the vent holes on the side of the
chassis near the DSP PCB, over the ampli-
fier module heatsink and out the rear
of the chassis.
5. Main DSP PCB, Mic Sense PCB and
Wall Plate PCB Removal
Note: There are three PCBs being removed
in this procedure. The largest of the three,
mounted in the bottom of the chassis, is the
Main DSP PCB. The Mic Sense and Wall
Plate PCB's can be detached once this
procedure is performed.
5.1 Disconnect the LED PCB ribbon cable at
J510 and the power/output ribbon cable at
JH501 from the Main DSP PCB (34).
5.2 Remove the six screws (2) that secure
the Main DSP PCB (34), Wall Plate PCB
(35) and the Mic Sense PCB (36) to the rear
panel.
5.3 Remove the two standoffs that secure
the RS232 connector to the rear panel.
5.4 Remove the two screws and washers
(38, 39) that secure the Main DSP PCB to
the bottom of the chassis (1) and carefully lift
all of the PCBs out of the unit together.
Re-assembly Notes:
- Be sure to replace both screws when re-
installing the DSP PCB. A connection to
chassis ground is made using these screws.
- Ensure that the insulating washer is re-
installed under the screw located near
connector P50 on the Main DSP PCB.
5.5 Make a note of the wiring configuration
and unplug the ribbon cables from J511 and
J512 on the Main DSP PCB.
5.6 Using needle-nose pliers, compress the
ends of the standoffs (37) that secure the
Main DSP PCB to the other two boards. Lift
off the boards.
6. Power Supply/Power Amp Module
Removal
Note: The Power Amplifier PCB Module
Assembly, with the attached heatsink, is to
be replaced as a single unit in the event of a
power amplifer PCB failure. Component
level repair of these PCBs is not recom-
mended due to reliability issues with lower
level repair.
6.1 Perform procedure 1.
6.2 Disconnect the large ribbon cable from
the Main DSP PCB (34) at JH501.
6.3 Remove the three screws (47) that
secure the power amplifier PCB module
assembly (33) to the chassis standoffs (48).
6.4 Remove the three nuts that secure the
heatsink assembly (42) to the chassis (1).
6.5 Remove the four screws (2) that secure
the power amplifier PCB module assembly
to the rear panel.
6.6 Slide the entire assembly forward while
lifting the front of the heatsink up slightly.
6.7 Disconnect the fan harness from the
connector on the bottom PCB assembly and
lift the heatsink assembly out of the chassis.
Disconnect the power transformer from the
lower amp PCB.
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