Servicing Components Mounted Directly On Heat Sinks; Servicing Metal Oxide Semiconductor (Mos) Devices - Ametek UPLC CU44-VER04 Applications Manual

UPLC™ Application Manual
6.5.4 Servicing Components
Mounted Directly on Heat
Sinks
1. Remove the heat sink and bracket from the
chassis by loosening the securing devices.
2. Remove the transistor, diode, or other device
from the heat sink.
3. When replacing the transistor, diode, or other
device, make certain that the device and the
heat sink make secure contact for good heat
dissipation. Mount a device first on the heat
sink, and then on the board. Also, make sure
that you replace all insulators, washers, spring
washers and other mounting hardware as you
originally found them.
We recommend a very light coating of DC-4
(Dow-Corning 4 Compound Silicon Lubri-
cant) in between transistors and diodes that
are mounted on heat sinks.
6.5.5 Servicing Metal Oxide
Semiconductor (MOS) Devices
MOS devices may be vulnerable to static changes.
Be sure to observe the special precautions
described below both before and during assembly.
Precautions to take before assembly:
• Avoid wearing silk or nylon clothing, as
this contributes to static buildup.
• Avoid carpeted areas and dry environ-
ments.
• Discharge body static by placing both
hands on a metal, earth-grounded surface.
Precautions to take during assembly to avoid the
possibility of electrostatic discharge:
• Wear a ground strap during assembly
• Avoid touching electrically-conductive cir-
cuit parts by hand
• When removing a module from the chassis,
always place it on a conductive surface
which is grounded through a resistance of
approximately 100 KΩ
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• Make sure that all electrically-powered test
equipment is properly grounded.
6.5.6 Transceiver NOVRAM Battery
A "Battery Failure" event indicates that the
Transceiver board's NOVRAM battery has
expired. The battery is a Dallas Semiconductor
DS9034PCX. And we recommend that you main-
tain a spare in stock. Some events may be lost if
this battery expires. It supplies power to an event
buffer.
Replacement consists of removing the plastic
cover from U30 on the Transceiver board. You
may need to gently pry it off with a small flathead
screwdriver. Replace the battery (observing the
polarity) and snap the plastic cover back onto
U30.
N O T E
Before touching a module with a test probe,
connect the ground lead from the test equip-
ment to the module. Always disconnect the
test probe before removing the ground lead
equipment.