Most spray circuit-coolants contain freon 12 as a
propellant. Because many freons adversely affect
switch contacts, check the contents and brand name
before using a spray coolant. Recommended circuit
coolant for the volts/division attenuators is isopropyl
alcohol.
Switch Contacts. Most of the switching in the 475 is
accomplished with circuit-board mounted, cam-actuated
contacts Care must be exercised to preserve the high-
frequency characteristics of these switches. Seldom is
switch cleaning necessary, but if it is required, observe the
following precautions.
TM 11-6625-2735-14-1
CRT Face, Filter and Shields.
Clean the Individual blue
or clear plastic implosion shields and the crt face with a
soft, Iint-free cloth dampened with denatured alcohol
(ethyl alcohol) or a mild detergent and water solution.
Install only one implosion shield between the bezel and crt
face. 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 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 Iow-pressure air
(approximately 9 lb/in
2
) to remove. Do not use tweezers or
other hard cleaning too Is 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.
Air Filter.
The air filter should be visually checked every
few weeks and cleaned or replaced if dirty. More frequent
inspections are required under severe operating con-
ditions. The following procedure is suggested for cleaning
the filter. If the filter is to be replaced, order new air filters.
For cleaning the switch contacts, isopropyl alcohol is
the recommended solvent to use. Apply the isopropyl
alcohol with a camel-hair brush. Do not use cotton swabs
as they tend to snag on contacts, possibly causing
damage, and leave strands of cotton, causing intermittent
electrical contact.
WARNING
Compressed air shall not be used for cleaning
purposes except where reduced to less than 29
pounds per square inch (psi) and then only with
effective chip guarding and personnel protective
equipment. Do no use compressed air to dry
parts when TRICHLOROTRI FLUOROETHAIVE has
been used. Compressed air is dangerous and
can cause serious bodily harm if protective
means or methods are not observed to prevent
chip or particle (of whatever size) from being
blown into the eyes or unbroken skin of the
operator of other personnel.
General Interior. Dust in the interior of the instrument
should be removed occasionally due to its electrical
conductivity
under high-humidity conditions. Ac-
cumulations of dirt should be removed as often as
operating conditions require because dirt can cause
overheating and component breakdown. Dirt on com-
ponents acts as an insulating blanket and prevents
efficient heat dissipation. It also provides an electrical
conduction path that can result in Instrument failure. The
best way to clean the interlor is to blow off the ac-
cumulated dust with dry, low-pressure air (approximately
9 Ib/in
2
). Remove any dirt that remains with a soft brush or
a cloth damped with a mild detergent and water solution. A
cotton-tipped applicator is useful for cleaning in narrow
spaces or for cleaning ceramic terminal strips and circuit
boards.
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 that remains can
be removed with a soft cloth dampened in a mild detergent
and water solution. Abrasive cleaners should not be used.
1. Remove the filter by pulling it out of the retaining
frame on the rear panel. Be careful not to drop any of the
accumulated dirt into the instrument.
2. Flush the loose dirt from the filter with a stream of
hot water.
3. Place the filter in a solution of mild detergent and
hot water and let it soak for several minutes.
4. Squeeze the filter to wash out any dirt which
remains.
5. Rinse the filter in clear water and allow it to dry.
6. Coat the dry filter with an air-filter adhesive.
7. Let the adhesive dry thoroughly.
8. Install the filter in the retaining frame.
4-5
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