Special Handling Of Static-Sensitive Devices; Case Cover And Shield Removal; Case Cover Removal; Analog Board Top Shield Removal - Keithley 2002 Repair Manual

Disassembly
• Remove the flux from the work areas when the repair
has been completed. Use pure water along with clean
foam-tipped swabs or a clean soft brush to remove the
flux. Be sure not to flush the flux across PC-boards
when removing flux or cleaning PC-boards with water.
• Once the flux has been removed, swab only the repaired
area with methanol, then blow dry the board with dry
nitrogen gas.
• After cleaning, the board should be allowed to dry in a
50°C low-humidity environment for several hours.
3.3 Special handling of static-sensitive de-
vices
CMOS devices operate at very high impedance levels for low
power consumption. As a result, any static that builds up on
your person or clothing may be sufficient to destroy these de-
vices, if they are not handled properly. Use the following pre-
cautions to avoid damaging them:
CAUTION
Many CMOS devices are installed in the
Model 2002. In general, it is recom-
mended that all semiconductor devices
be handled as being static-sensitive.
1. ICs should be transported and handled only in contain-
ers specially designed to prevent static build-up. Typi-
cally, these parts will be received in anti-static
containers of plastic or foam. Keep these devices in their
original containers until ready for installation.
2. Remove the devices from their protective containers
only at a properly grounded work station. Also, ground
yourself with a suitable wrist strap.
3. Handle the devices only by the body; do not touch the
pins.
4. Any printed circuit board into which the device is to be
inserted must also be grounded to the bench or table.
5. Use only anti-static type solder sucker.
6. Use only grounded tip solder irons.
7. Once the device is installed in the PC board, it is normal-
ly adequately protected, and normal handling can re-
sume.
3.4

Case cover and shield removal

If it is necessary to troubleshoot the instrument or to replace
a component, use the following procedures as required. The
first procedure removes the case cover, and the second pro-
3-2
cedure removes the top shield of the analog board, allowing
access to analog circuitry.

3.4.1 Case cover removal

WARNING
Before removing the case cover, discon-
nect the line cord and any test leads
from the instrument.
To remove the case cover, refer to drawing 2002-054 (at the
end of this section), and perform the following steps:
1. Remove Handle: The handle serves as an adjustable
tilt-bail. Its position is adjusted by gently pulling it away
from the sides of the instrument case and swinging it up
or down. To remove the handle, swing the handle below
the bottom surface of the case and back until the orien-
tation arrows on the handles line up with the orientation
arrows on the mounting ears. With the arrows lined up,
pull the ends of the handle out of the case.
2. Remove Mounting Ears: Each mounting ear is secured
to the chassis with a single screw. Remove the two
screws, and pull down and out on each mounting ear.
Note: When re-installing the mounting ears, make sure
to mount the right ear to the right side of the chassis, and
the left ear to the left side of the chassis. Each ear is
marked "RIGHT" or "LEFT" on its inside surface.
3. Remove Rear Bezel: The rear bezel is secured to the
chassis by two captive screws. To remove the rear bezel,
loosen the two screws, and pull the bezel away from the
case.
4. Remove Grounding Screw: Remove the grounding
screw for the case cover. This screw is located on the
bottom side of the instrument at the rear.
5. Remove Chassis: Grasp the front bezel of the instru-
ment and carefully slide the chassis forward, out of the
metal case.
The internal PC-board assemblies are now accessible.

3.4.2 Analog board top shield removal

Most of the analog circuitry is located under the top shield
for the analog board. The top shield (shown in drawing 2002-
050) is secured to the analog board by a single screw. To re-
move the top shield, simply loosen the screw, and carefully
lift the shield out of the chassis. You should remove the rear
choice first and may have to remove the front choke as well
to prevent damage.