Section 4—492/492P Service Vol. 1
MAINTENANCE
Introduction
This section describes the procedure for reducing or pre
venting instrument malfunction, plus troubleshooting, and
corrective maintenance. Preventive maintenance improves
instrument reliability. Should the instrument fail to function
properly, corrective measures should be taken immediately;
otherwise, additional problems may develop within the
instrument.
Static-Sensitive Components
Static discharge can damage any semiconductor
component in this instrument.
This instrument contains electrical components that are
susceptible to damage from static discharge. See Table 4-1
for relative susceptibility of various classes of semi
conductors. Static voltages of 1 kV to 30 kV are common in
unprotected environments.
Observe the following precautions to avoid damage:
1) minimize handling of static-sensitive components;
2 ) transport and store static-sensitive components or as
semblies in their original containers, on a metal rail, or on
conductive foam. Label any package that contains static-
sensitive assemblies or components;
3) discharge the static voltage from your body by wearing a
grounded wrist strap while handling these components. Ser
vicing static-sensitive assemblies or components should be
performed only at a static-free work station by qualified ser
vice personnel;
4) nothing capable of generating or holding a static charge
should be allowed on the work station surface;
5) keep the component leads shorted together whenever
possible;
6 ) pick up components by the body, never by the leads;
7) do not slide the components over any surface;
8 ) avoid handling components in areas that have a floor or
work-surface covering capable of generating a static
charge;
9) use a soldering iron that is connected to earth ground;
1 0 ) use only special anti-static suction type or wick type
desoldering tools.
Table 4-1
RELATIVE SUSCEPTIBILITY TO STATIC DISCHARGE
DAMAGE
Semiconductor Classes
Relative
Susceptibility
Levels®
MOS or CMOS microcircuits
or discretes, or linear microcircuits
with MOS inputs. (Most Sensitive)
1
ECL
2
Schottky signal diodes
3
Schottky TTL
4
High-frequency bipolar transistors 5
JFETs
6
Linear microcircuits
7
Low-power Schottky TTL 8
TTL (Least Sensitive) 9
‘ Voltage equivalent for levels:
1 = 100 to 500 V 4 = 500 V 7 = 400 to 1000 V (ext)
2 = 200 to 500 V 5 = 400 to 600 V 8 = 900 V
3 = 250 V 6 = 600 to 800 V 9 = 1200 V
(Voltage discharged from a 100 pF capacitor through a resis
tance of 100 Ω.)
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