6-10 REMOVING AND
REPLACING THE REAR
PANELASSEMBLY
This paragraph provides instructions for removing and replacing the
rear panel assembly of the 682XXB/683XXB. The rear panel assembly
contains the A21 Line Filter/Rectifier PCB, the A21-1 BNC/AUX I/O
Connector PCB, the line module assembly,and the fan assembly. Refer
to Figure 6-4 during this procedure.
Preliminary Disconnect the power cord from the unit and remove
the chassis covers as described in paragraph 6-2.
WARNING
When power is removed from the instrument, always allow
five minutes for the capacitors on the A21 Line Filter/Recti-
fier PCB to discharge before removing the rear panel assem-
bly.
Procedure Remove and replace the rear panel assembly as fol-
lows:
Step 1 Using a Phillips screwdriver,remove the
screw on the top of the rear panel assem-
bly that fastens the rear panel assembly
to the bracket attached to the power sup-
ply housing.
Step 2 Turnthe instrument upside down.
Step 3 Remove the three screws from the rear
panel assembly.(One screw fastens the
rear panel assembly to the bracket at-
tached to the power supply housing; the
other two screws attach the rear panel as-
sembly to the Motherboard.)
Step 4 Return the instrument to the upright po-
sition.
Step 5 Remove the screws attaching the rear
panel assembly to the chassis sides.
Step 6 Using a 716-inchwrench, disconnect the
coaxial cables (W110,W109, and W130)
going to the rear panel 10 MHz REF IN,
10 MHz REF OUT,and FM IN BNC con-
nectors.
Step 7 Disconnect the coaxial cables W127,
W128, and W129 from the A21-1 PCB by
lifting up on the cable connectors.
Step 8 Remove the power supply cover and set it
aside.

682XXB/683XXB MM 6-13

REMOVAL AND REAR PANEL

REPLACEMENT PROCEDURES ASSEMBLY