Tektronix 7A22, Instruction Manual, Page: 36 / 99

Type
7A22
SEcr. N4
MAINTENANCE
Change information, if any, affecting this section will be found at the
rear of the manual.
Introduction
Information which will aid in keeping the Type
7A22
op­
erating at its peak performance is contained in this section.
Cleaning, lubricating and visual inspection hints are included
under preventative maintenance. The section on corrective
maintenance includes troubleshooting and corrective pro­
cedures. Parts identification and soldering techniques are
included where necessary.
PREVENTIVE MAINTENANCE
General
The instrument should be cleaned, inspected and recali­
brated at regular intervals. The recommended interval for
average operating conditions is every
6 months or every
1000 hours of operation, whichever occurs first.
Cleaning the Front Panel
Loose dust may be removed with cloth and a dry paint
brush. Water and mild detergents such as Kelite or Spray
White may be used.
CAUTION
Avoid the use of chemical agents which might
damage the plastics used in this unit. Avoid chemi­
cals such as benzene, toluene, xylene, acetone or
similar solvents.
Cleaning the Interior
Cleaning of the interior of the unit should precede cali­
bration, since the cleaning process might alter the settings of
the calibration adiustments.
To clean the interior, use low-velocity compressed air to
blow off the accumulated dust. High velocity air streams
should be avoided to prevent damage to components.
®I
WARNING
Use an eye-shield when cleaning with pressurized
air. Hardened dirt can be removed with a paint
brush, cotton tipped swab or cloth dampened with
a water and mild detergent solution. Avoid the use
of chemical cleaning agents that might damage
the plastic parts.
Visual Inspection
The unit should be inspected occasionally for such defects
as poor connections, broken or damaged circuit boards, im­
properly seated transistors and heat-damaged parts. The
remedy for most visible defects is obvious. However, damage
from overheating is usually a symptom of less obvious trouble;
and unless the cause is determined before parts are replaced
the damage may be repeated.
Transistor Checks
Periodic preventive maintenance checks on the transistors
used in the unit are not recommended. The circuits within
the unit generally provide the most satisfactory means of
checking transistors usability. Performance of the circuits is
thoroughly checked during recalibration, and substandard
transistors will usually be detected at that time.
Calibration
To insure accurate measurements, the Type 7 A22 calibra­
tion should be checked after each 1000 hours of operation or
every six months if used intermittently. Complete calibration
instructions are contained in Section
5.
The calibrated procedure can be helpful in isolating
major troubles in the unit. Moreover, minor troubles not
apparent during regular operation may be revealed and
corrected during calibration.
CORRECTIVE MAINTENANCE
General
Replacement of some parts in the unit should be done
by following a definite procedure. Some procedures, such
as soldering and replacing components on the circuit boards,
are outlined in this portion of the manual.
Many electrical components are mounted in a particular
way to reduce or control stray capacitance and inductance.
When selecting replacement parts, it is important to remem­
ber that the physical size and shape of a component may
affect its performance at high frequencies. When a repair
is made, calibration and performance of the relevant por­
tions of the circuit should be checked. Refer to Table 4-1
and to the Performance Check/Calibration procedure in
Section
5
and perform the applicable steps.
4-1