6-11 REMOVING AND
REPLACING THE
A21 PCB
This paragraph provides instructions for removing and replacing the
A21 Line Filter/Rectifier PCB, which is located on the rear panel as-
sembly (see Figure 6-4).
Preliminary Disconnect the power cord from the unit. Remove
the chassis covers as described in paragraph 6-2.
Remove the rear panel assembly as described in
paragraph 6-10.
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 A21 PCB as follows:
Step 1 Using a Phillips screwdriver,remove the
four screws that fasten the A21 shield to
the A21 PCB.
Step 2 Remove the shield and set it aside.
Step 3 Disconnect the cables connected to P1,
P2, and P6 on the PCB.
Step 4 Using a Phillips screwdriver,remove the
four screws that fasten the PCB to the
rear panel assembly and set aside.
Step 5 Remove the PCB from the rear panel as-
sembly.
Step 6 Toreplace the PCB, reverse the removal
process.

6-16 682XXB/683XXB MM

REMOVAL AND

REPLACEMENT PROCEDURES A21 PCB