Maintenance; Preventive Maintenance; General; Cleaning - Tektronix 7B92 Instruction Manual

Section 3-7892 Service
MAINTENANCE
This section of the manual contains maintenance information for use in preventive maintenance, corrective maintenance,
and troubleshooting of the 7892.
PREVENTIVE MAINTENANCE
General
Preventive maintenance consists of cleaning, visual
inspection, lubrication, etc. Preventive maintenance per·
formed on a regular basis may prevent instrument break·
down and will improve the reliability of this instrument.
The severity of the environment to which the 7892 is
subjected determines the frequency of maintenance. A
convenient time to perform preventive maintenance is
preceding recalibration of the instrument.
Cleaning
The 7892 should be cleaned as often as operating
conditions require. Accumulation of dirt in the instrument
can cause overheating and component breakdown. Dirt on
components acts as an insu lating blanket and prevents
efficient heat dissipation. It may also provide an electrical
conduction path.
The covers of the oscilloscope reduce the amount of
dust that reaches the interior of the 7892. Operation of the
system without the oscilloscope covers in place necessitates
more frequent cleaning. When the 7892 is not in use, it
should be stored in a protected location, such as a
dust-tight cabinet.
Avoid the use of chemical agents which might damage
the plastics used in this instrument. Avoid chemicals
which contain benzene, toluene, xylene, acetone, or
similar solvents.
Exterior. Loose dust accumulated on the outside of the
7892 can be removed with a soft cloth or small paint brush.
The paint brush is particularly useful for dislodging dirt on
and around the front-panel controls. Dirt that remains can
be removed with a soft cloth dampened in a mild detergent
and water solution. Abrasive cleaners should not be used.
Interior. Dust in the interior of the instrument should
be removed occasionally, due to its electrical conductivity
under high-humidity conditions. The best way to clean the
interior is to blow off the accumulated dust with dry
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low-velocity air. Remove any dirt that remains with a soft
paint brush or a cloth dampened with a mild detergent and
water solution. A cotton-tipped applicator
IS
useful for
cleaning in narrow spaces.
Visual Inspection
The 7892 should be inspected occasionally for such
defects as broken connections, broken or damaged circuit
boards, improperly seated transistors or relays, and heat-
damaged parts.
The corrective procedure for most visible defects is
obvious; however, particular care must be taken if heat-
damaged components are found. Overheating usually
indicates other trouble in the instrument; therefore, it is
important that the cause of overheating be corrected to
prevent recurrence of the damage.
Semiconductor Checks
Periodic checks of the transistors, FEr's, and IC's used
in the 7892 are not recommended. The best indication of
performance is the actual operation of the device in the
circuit. Performance of the circuits is thoroughly checked
during recalibration; substandard semiconductors will
usually be detected at that time.
Recal ibration
To ensure accurate measurements, check the calibration
of this instrument each 1000 hours of operation or every
six months if used infrequently. In addition, replacement of
components may necessitate recalibration of the affected
circuits. Calibration instructions are given in Section 4.
TROUBL ESHOOTI NG
Introduction
The following information is provided to facilitate
troubleshooting of the 7892. I nformation contained in
other sections of this manual should be used along with the
following information to aid in locating the defective
component. An understanding of the circuit operation is
very helpful in locating troubles. See the Circuit Descrip-
tion section.
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