Maintenance—475
Most spray circuit coolants and contact cleaners contain
Freon 12 as a propellant. Because many Freons adversely
affect the contacts, check the contents before using a spray
cleaner or coolant. No Noise (Electronic Chemical) is an
acceptable contact cleaner-restorer. The only recommended
circuit coolants are dry ice or isopropyl alcohol. There are
three recommended switch lubricants. They are Silicone
Versilube (General Electric Co.), Rykon R (Standard Oil),
and WD-40 (Rocket Chemical Co.).
Exterior. Loose dust accumulated on the outside of the
475 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 which remains
can be removed with a soft cloth dampened in a mild
detergent and water solution. Abrasive cleaners should not
be used.
CRT. Clean the blue and clear plastic light filters and
the CRT face with a soft, lint-free cloth dampened with
denatured alcohol or a mild detergent and water solution.
The optional CRT mesh filter can be cleaned in the
following manner.
1. Hold the filter in a vertical position and brush lightly
with a soft No. 7 watercolor brush to remove light coatings
of dust and lint.
2. Greasy residues or dried-on dirt can be removed with
a solution of warm water and a neutral pH liquid detergent.
Use the brush to lightly scrub the filter.
3. Rinse the filter thoroughly in clean water and allow
to air dry.
4. If any lint or dirt remains, use clean low-pressure air
to remove. Do not use tweezers or other hard cleaning tools
on the filter as the special finish may be damaged.
5. When not in use, store the mesh filter in a lint-free
dust-proof container such as a plastic bag.
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,
low-pressure 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 or for cleaning circuit boards.
Lubrication
The fan motor and most of the potentiometers used in
the 475 are permanently sealed and generally do not
require periodic lubrication. The switches used in the 475,
both cam- and lever-type, are installed with proper lubrica
tion applied where necessary and will only rarely require
any additional lubrication. It is recommended that a regular
periodic lubrication program not be performed on any of
the components used in the 475.
Transistor Checks
Periodic checks of the transistors and other semi
conductors in the 475 are not recommended. The best
check of semiconductor performance is actual operation in
the instrument.
Recalibration
To assure accurate measurements, check the calibration
of this instrument after each 1000 hours of operation or
every six months if used infrequently. In addition, replace
ment of components may necessitate recalibration of the
affected circuits. Complete calibration instructions are
given in the Calibration section.
The calibration procedure can also be helpful in local
izing certain troubles in the instrument. In some cases,
minor troubles may be revealed or corrected by recalibra
tion.
CORRECTIVE MAINTENANCE
General
Corrective maintenance consists of component replace
ment and instrument repair. Special techniques required to
replace components in this instrument are given here.
Obtaining Replacement Parts
Standard Parts. All electrical and mechanical part re
placements for the 475 can be obtained through your local
TEKTRONIX Field Office or representative. However,
many of the standard electronic components can be
obtained locally in less time than is required to order them
from Tektronix, Inc. Before purchasing or ordering replace
ment parts, check the parts list for value, tolerance, rating,
and description.
NOTE
When selecting replacement parts, it is important to
remember that the physical size and shape of a
component may affect its performance in the instru-
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