Keithley 7070, Instruction Manual

Page: 58 / 73

SECTION 4
Service Information
4-1
4.1 INTRODUCTION
This section contains information necessary to service the
Model 7070 Universal Adapter Card and is arranged as
follows:
4.2 Handling and Cleaning Precautions: Discusses han-
dling precautions and methods to clean the card
should it become contaminated.
4.3 Special Handling of Static-Sensitive Devices:
Reviews precautions necessary when handling static-
sensitive devices.
4.4 Troubleshooting: Presents some troubleshooting tips
of the Model 7070.
4.5 Principles of Operation: Brie ß y discusses circuit
operation.
4.2 HANDLING AND CLEANING PRECAUTIONS
Care should be taken when handling or servicing the card to
prevent possible contamination. The following precautions
should be taken when servicing the card.
1. Handle the card only by the edges and handle. Do not
touch any board surfaces or components not associated
with the repair.
2. Do not store or operate the card in an environment
where dust could settle on the circuit board. Use dry
nitrogen gas to clean dust off the board if necessary.
3. After soldering on the circuit board, remove the ß ux
from the work areas when the repair has been com-
pleted. Use Freon TMS or TE or the equivalent along
with clean cotton swabs or a clean, soft brush to remove
the
ß ux. Take care not to spread the ß ux to other areas
of the circuit board. Once the ß ux has been removed,
swab only the repaired area with methanol, then blow
dry the board with dry nitrogen gas.
4. After cleaning, the card should be placed in a 50°C low-
humidity environment for several hours before use.
4.3 SPECIAL HANDLING OF STATIC-SENSITIVE
DEVICES
CMOS and other high-impedance devices are subject to
possible static discharge damage because of the high-
impedance levels involved. When handling such devices,
use the precautions listed below.
NOTE
In order to prevent damage, assume that all parts
are static-sensitive.
1. Such devices should be transported and handled only
in containers specially designed to prevent or dissipate
static build-up. Typically, these devices will be received
in anti-static containers made of plastic or foam. Keep
these parts in their original containers until ready for
installation or use.
2. Remove the devices from their protective containers
only at a properly-grounded work station. Also ground
yourself with an appropriate wrist strap while working
with these devices.
3. Handle the devices only by the body; do not touch the
pins or terminals.
4. Any printed circuit board into which the device is to be
inserted must Þ rst be grounded to the bench or table.
5. Use only static-sensitive type de-soldering tools and
grounded-tip soldering irons.
4.3.1 Rear Shield
Copper cladding has been added to the rear shield of the
matrix card in order to provide increased protection from
static discharge. The copper shield is electrically connected
to chassis ground of the matrix card by a jumper wire.
In order to service the matrix card, it may be necessary to
remove the rear shield. Referring to Figure 4-1, perform the
following procedure to remove and reinstall the rear shield:
1. Disconnect the jumper wire from the matrix card chas-
sis. The wire is secured to the matrix card chassis with a
screw.
2. The rear shield is secured to the matrix card by eight
standoffs. Carefully slide the rear shield upward until
the eight standoffs align with the large clearance holes
in the shield and remove the shield.
3. To reinstall the shield, reverse the above procedure.
Make sure the metal side of the shield is facing
outward.