tion (such as Kelite or Spray White). Abrasive cleaners
should not be used.
This section of the manual pertains to the maintenance
and troubleshooting of the Type 491. The first portion of
the section describes some general preventive measures to
Do not permit water to get inside controls or shaft
help minimize major problems. This is followed with some
Avoid the use of chemical cleaning
corrective maintenance information and information on order-
agents which might damage the plastics used in
ing parts or components. The last and major portion of the
this instrument. Some chemicals to avoid are ben-
section describes the removal and replacement of the sub-
zene, toluene, xylene, acetone or similar com-
assemblies and their components, and some general trouble-
shooting information pertinent to the Type 491. Trouble
symptoms and possible causes are not listed for this instru-
The CRT faceplate, protector plate and filters are as
ment because all circuits are interrelated. Listed causes for
various troubles could cause confusion. However one mis-
leading trouble symptom may occur when one of the three
Clean the plastic light filters, faceplate protector and the
CRT face with a soft, lint-free cloth dampened with de-
from the phase lock circuit and prevent vertical trace shift
natured alcohol. The CRT mesh filter is easily scratched or
as the FINE RF CENTER FREQ control is adjusted which
damaged. It should be cleaned as follows:
indicates trouble in the phase lock circuit.
1. Hold the filter in a vertical position and brush lightly
with a soft water-color brush to remove light coatings of
dust or lint.
Removing or replacing the dust cover for the
instrument may be hazardous, if the instrument
2. Greasy residues or dried-on dirt are removed with a
is lifted out of, or slid into the dust cover. Remove
solution of warm water and a neutral liquid detergent. Use
or replace the cover as follows: Place the acces-
the water-color brush to scrub the filter.
sory cover on the instrument, Set the instrument
3. Rinse the filter thoroughly in clean water and allow
on the front-panel cover (do not set the instru-
to air dry.
ment on the front-panel controls). The dust cover
may now be removed or replaced with safety and
4. If any lint or dirt remains, use clean low-pressure air
to remove. Do not use tweezers or other sharp cleaning
tools on the filter as the special finish may be damaged.
5. Store the mesh filter in a lint-free, dust-proof container
such as a plastic bag.
Preventive maintenance consists of cleaning, visual inspec-
tion, lubrication, and if needed, recalibration. Preventive
Do not write on the CRT face--use the clean
maintenance is generally more economical than corrective
plastic protector plate mounted in the ornamental
maintenance, since it can usually be done at a time con-
venient to the user. The preventive maintenance schedule
established for the instrument should be based on the amount
of use and the environment in which the instrument is used.
The life of potentiometers and selector switches is increased
if these devices are kept properly lubricated. Use a clean-
ing type lubricant (such as Cramoline) on shaft bushings
Clean the instrument often enough to prevent accumula-
and switch contacts. Lubricate the switch detents with a
tion of dirt, Dirt on the components acts as a thermal insu-
heavier grease (Beacon grease No. 325 or equivalent). Do
lating blanket (preventing efficient heat dissipation) and may
not over-lubricate. The necessary materials and instructions
provide electrical conducting paths.
for proper lubrication of Tektronix instruments are contained
Clean the instrument by loosening the accumulated dust
in a component lubrication kit which may be ordered from
with a dry, soft paint brush. Remove the loosened dirt by
Tektronix. Order Tektronix Part No. 003-0342-00.
vacuum and/or dry low pressure compressed air (high veloc-
The dial and tuning assembly should be lubricated period-
ity air can damage certain components. ) Hardened dirt and
ically. This is normally every 500 hrs., however if the tuning
grease may be removed with a cotton-tipped swab or a
tends to bind or drag it may be due to improper lubrication.
soft cloth dampened with water and a mild detergent solu-