6-4
c.
The transformer is secured to the bottom of the
chassis by four screws. Remove these screws and
pull the transformer out of the chassis.
4. Remove AC power receptacle: Remove the AC power
receptacle as follows:
a.
Disconnect the receptacle ground wire. A kep nut is
used to connect this green ground wire to a threaded
stud on the chassis.
b. Unplug the AC power receptacle cable. The connec-
tor for this cable is located on the analog board next
to the power receptacle.
c.
A spring clip on each side of the receptacle is used
to secure it to the rear panel of the chassis. To
remove it, press both clips inward and, at the same
time, push the receptacle out of the access hole in
the rear panel of the chassis.
5. Unplug cable to digital board: On the left side of the
analog board there is a ribbon cable going to the digital
board. Turn the chassis upside-down, and unplug this
cable at connector J1029 on the digital board. Return the
chassis to the right-side-up position.
6. Disconnect input/output cables: Disconnect the follow-
ing cables from the analog board:
a.
INPUT cable at J1019 and J1020.
b. V SOURCE cable at J1022.
c.
PREAMP OUT, COMMON, and 2V OUTPUT
cable at J1021.
7. Unfasten analog board: The analog board is secured to
the chassis at the rear panel by the two BNC connectors
(External Trigger and Meter Complete). At the rear
panel, remove the nuts and lock washers for the BNC
connectors. Also remove the two screws that secure the
board to the chassis.
8. Remove analog board: The board is held in place by
edge guides on each side of the chassis. Slide the analog
board forward until the board edges clear the guides, and
then carefully lift the board out of the chassis. The bot-
tom shield on the analog board can be removed by sim-
ply pulling it off the board.
6.6
Front panel disassembly
Use the following disassembly procedure to remove the dis-
play board and/or the pushbutton switch pad. Drawing
6517A-054 shows how the front panel separates from the
chassis, and drawing 6517A-040 shows an exploded view of
the front panel assembly.
NOTE
Before performing the following proce-
dure to remove and disassemble the front
panel, remove the case cover as explained
in paragraph 6.4.
Perform the following steps to remove and disassemble the
front panel:
1. Unplug display cable: Turn the chassis upside-down,
and unplug the display cable from the digital board at
connector J1033.
2. Remove front panel assembly: The front panel assembly
has four retaining clips that snap onto the chassis over
four pem nut studs. Two retaining clips are located on
each side of the front panel. Pull the retaining clips out-
ward and, at the same time, pull the front panel assembly
forward until it separates from the chassis.
3. Remove display board: The display board is held in
place by a PC board stop. This stop is simply a plastic
bar that runs along the bottom edge of the display board.
Using a thin bladed screwdriver, pry the plastic bar
upward until it separates from the casing of the front
panel. Pull the display board out of the front panel.
4. Remove switch pad: The conductive rubber switch pad
simply pulls out of the front panel.
6.7
Main CPU firmware replacement
Changing the firmware may be necessary as upgrades
become available. The firmware revision level for the main
CPU is displayed during the power-on sequence. The firm-
ware for the main CPU is located in two ROMs (U637 and
U638) located on the digital board. (See the digital board
component layout drawing 6517-140 at the end of Section
4.)
Perform the following steps to replace the CPU firmware:
WARNING
Disconnect the instrument from the
power line, and disconnect all cables
and test leads before changing the
firmware.
1. Remove the case cover as explained in paragraph 6.4.
2. Turn the instrument upside down to gain access to the
digital board.
3. Locate U637 and U638 (ROMs) on the digital board.
These two ICs are located near the center of the PC
board next to the power transformer.