Solder Repairs; Special Handling Of Static-Sensitive Devices; Case Cover Removal; Pc Board Removal - Keithley 6517 Service Manual

Disassembly

6.2.2 Solder repairs

Observe the following precautions when it is necessary to
use solder on a circuit board:
• Use an OA-based (non-acid) flux, and take care not to
spread the flux to other areas of the circuit board.
• 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 wash contaminated flux or water
over other PC board areas.
• 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.
6.3 Special handling of static-sensitive
devices
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
devices, if they are not handled properly. Use the following
precautions to avoid damaging them:
CAUTION
Many CMOS devices are installed in the
Model 6517A. 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 usually
adequately protected, and normal handling can resume.
6-2
6.4

Case cover removal

If it is necessary to troubleshoot the instrument or to replace
a component, use the following procedure to remove the case
cover.
WARNING
Before removing the case cover, discon-
nect the line cord and any connecting
cables and wires from the instrument.
Allow sufficient time for capacitors to
discharge before disconnecting cables or
removing the cover.
To remove the case cover, refer to drawing 6517A-057 (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 chas-
sis by two 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 instrument
and carefully slide the chassis forward out of the metal
case.
The internal PC board assemblies are now accessible.
6.5

PC board removal

There are three PC boards mounted in the chassis: the digital
board, the analog board, and the A/D converter board, which
is mounted on the analog board. The removal of these three
boards is covered below. The display board is mounted in the