Tektronix PG 508, Инструкция по эксплуатации

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TM 11-6625-2980-14
known to be operating properly. If the trouble persists
after substitution, then the power module is probably at
fault. Moving a properly operating plug-in from
compartment to compartment will help determine if one
or more compartments has a problem.
Visual Check
Inspect the portion of the system in which the
trouble is suspected. Many troubles can be located by
visual clues such as unsoldered connections, broken
wires, damaged circuit boards, damaged components,
etc.
Instrument Calibration
Check the calibration of the suspected plug-in
module or the affected circuit if the trouble is obviously
in a certain circuit. The trouble may only be a result of
misadjustment or may be corrected by re-calibration.
Complete calibration instructions are given in TB 11-
6625-2980-35.
Circuit Isolation
Note the symptom. It often identifies the circuit in
which the trouble is located. When trouble symptoms
appear in more than one circuit, check the affected
circuits by making waveform and voltage
measurements.
Incorrect operation of all circuits often means
trouble in the power supplies. Using a multimeter, check
first for correct voltages of the individual regulated
supplies according to the plug-in module schematics
and calibration procedures. Then check the unregulated
supplies of the power modules. Defective components
elsewhere in the instruments can appear as power
supply problems. In these instances, suspected circuits
should be disconnected from apparently bad power
supplies one at a time to narrow the search.
Voltages and Waveforms
Often defective components can be located by
using waveform and voltage indications when they
appear on the schematic or in the calibration
procedures. Such waveforms and voltage labels are
typical indications and will vary between instruments. To
obtain operating conditions similar to those used to take
these readings, refer to the first diagram in the service
sections.
Component Checking
If a component cannot be disconnected from its
circuit, then the effects of the associated circuitry must
be considered when evaluating the measurement.
Except for soldered in transistors and integrated circuits,
most components can be lifted at one end from the
circuit board.
Transistors and IC's. Turn the power switch off
before removing or replacing any semiconductor.
A good check of transistor operation is actual
performance under operating conditions. A transistor
can most effectively be checked by substituting a new
component for it (or one which has been checked
previously). However, be sure that circuit conditions are
not such that a replacement transistor might also be
damaged. If substitute transistors are not available, use
a dynamic tester. Static-type testers are not
recommended, since they do not check operation under
simulated operating conditions. A suction-type
desoldering tool must be used to remove soldered-in
transistors; see component replacement procedure for
details.
Integrated circuits can be checked with a voltmeter,
test oscilloscope, or by direct substitution. A good
understanding of the circuit description is essential to
troubleshooting circuits using IC's. Operating
waveforms, logic levels, and other operating information
for the IC's are given in the circuit description
information of the appropriate manual. Use care when
checking voltages and waveforms around the IC's so
that adjacent leads are not shorted together. A
convenient means of clipping a test probe to the 14- and
16-pin in-line IC's is with an integrated-circuit test clip.
This device also doubles as an extraction tool.
Diodes. Do not use an ohmmeter that has a high
internal current. High currents may damage the diode.
A diode may be checked for an open or shorted
condition by measuring the resistance between
terminals. With an ohmmeter scale having an internal
source of between 800 mV and 3 V, the resistance
should be very high in one direction and very low when
the leads are reversed .
Resistors. Check the resistors with an ohmmeter.
Resistor tolerances are given in the Electrical Parts List
in every manual. Resistors do not normally need to be
replaced unless the measured value varies widely from
the specified value.
Capacitors. A leaky or shorted capacitor can be
detected by checking resistance with an ohmmeter on
the highest scale. Use an ohmmeter which will not
exceed the voltage rating of the capacitor. The
resistance reading should be high after initial charge of
the capacitor. An open capacitor can best be detected
with a capacity meter, or by checking whether it passes
AC signals.
A-9