Maintenance—492/492P Service Vol. 1 (SN B030000 & up)
After cleaning, carefully check the instrument for such
defects as defective connections, damaged parts, and im
properly seated transistors and integrated circuits. The rem
edy for most visible defects is obvious. If heat-damaged
parts are discovered, try to determine the cause of
overheating before the damaged part is replaced; other
wise, the damage may be repeated.
Visual Inspection
Transistor and Integrated Circuit Checks
Periodic checks of the transistors and integrated circuits
are not recommended. The best measure of performance is
the actual operation of the component in the circuit. Perfor
mance of these components is thoroughly checked during
the performance check or recalibration; any sub-standard
transistors or integrated circuits will usually be detected at
that time.
When handling MOS FET’s, keep the shorting strap in
place until the transistor is in its socket.
Performance Checks and Recalibration
The instrument performance should be checked after
each 1 0 0 0 hours of operation or every six months if the
instrument is used intermittently to ensure maximum perfor
mance and assist in locating defects that may not be appar
ent during regular operation. Instructions for conducting a
performance check are provided in the Performance Check
part of the Calibration section.
TROUBLESHOOTING
The following are a few aids and suggestions that may
assist in locating a problem. After the defective assembly or
component has been located, refer to the Corrective Main
tenance part of this section for removal and replacement
instructions.
Wiring Color Code. Color coded wires are used to aid
circuit tracing. Power supply dc voltage leads have either a
red background for positive voltage or a violet background
for negative voltage. Signal wires and coaxial cables use an
identifying one-band or two-band color code.
Troubleshooting Aids
Diagrams. Block and circuit diagrams, on foldout pages
in the Diagrams section, contain any significant waveform,
voltage, and logic data information. Any necessary informa
tion as to how the data was acquired, such as operational
state of the instrument, is provided on the diagram or adja
cent to it. Refer to the Replaceable Electrical Parts list sec
tion for a description of all assemblies and components.
NOTE
Corrections and modifications to the manual and in
strument are described on inserts bound Into the rear
of the manual. Check this section for changes and
corrections to the manual or the instrument.
Circuit Board Illustrations. Electrical components, con
nectors, and test points are identified on circuit board illus
trations located on the inside fold of the corresponding
circuit diagram or the back of the preceding diagram. A grid
on the circuit board illustrations and the circuit schematic
plus a look-up table, provides the means to quickly locate
components on either diagram.
Multiple Terminal (Harmonica) Connectors. Some
intercircuit connections are made through pin connectors
that may be mounted in a harmonica type holder. The termi
nals in the holder are identified by numbers that appear on
the holder and the circuit diagrams. Connector orientation to
the circuit board is keyed by triangles on the holder and the
circuit board (see Fig. 4-1). In some cases, the triangle or
arrow is screened on the chassis adjacent to the connector.
Some connectors contain more than one section. Connec
tors are identified on the schematic and board with a “P" or
■J’ .
Resistor Values. Many types of resistors (such as com
position, metal film, tapped, thick film resistor network pack
age, plate, etc.) are used in the 492/492P. The value is
either color coded in accordance with the EIA color code, or
printed on the body of the component.
Capacitor Marking. The capacitance value of ceramic
disc plate and slug capacitors or small electrolytics are
marked in microfarads on the side of the component body.
The ceramic tubular capacitors and feedthrough capacitors
are color coded in picofarads. Tantalum capacitors are color
coded as shown in Fig. 4-2.
REV AUG 1981
4-3
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