Tektronix 491, Руководство по обслуживанию

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SECTION 4
MAINTENANCE
Introduction
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
help minimize major problems. This is followed with some
corrective maintenance information and information on order-
ing parts or components. The last and major portion of the
section describes the removal and replacement of the sub-
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-
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
varactor diodes short. This will clamp the DC output voltage
from the phase lock circuit and prevent vertical trace shift
a s t h e F I N E R F C E N T E R F R E Q c o n t r o l i s a d j u s t e d w h i c h
indicates trouble in the phase lock circuit.
C A U T I O N
R e m o v i n g o r r e p l a c i n g t h e d u s t c o v e r f o r t h e
i n s t r u m e n t m a y b e h a z a r d o u s , i f t h e i n s t r u m e n t
is lifted out of, or slid into the dust cover. Remove
or replace the cover as follows: Place the acces-
s o r y c o v e r o n t h e i n s t r u m e n t , S e t t h e i n s t r u m e n t
o n t h e f r o n t - p a n e l c o v e r ( d o n o t s e t t h e i n s t r u -
ment on the front-panel controls). The dust cover
may now be removed or replaced with safety and
ease.
PREVENTIVE MAINTENANCE
General
Preventive maintenance consists of cleaning, visual inspec-
tion, lubrication, and if needed, recalibration. Preventive
maintenance is generally more economical than corrective
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.
Cleaning
Clean the instrument often enough to prevent accumula-
tion of dirt, Dirt on the components acts as a thermal insu-
lating blanket (preventing efficient heat dissipation) and may
provide electrical conducting paths.
Clean the instrument by loosening the accumulated dust
with a dry, soft paint brush. Remove the loosened dirt by
vacuum and/or dry low pressure compressed air (high veloc-
ity air can damage certain components. ) Hardened dirt and
grease may be removed with a cotton-tipped swab or a
soft cloth dampened with water and a mild detergent solu-
t i o n ( s u c h a s K e l i t e o r S p r a y W h i t e ) . A b r a s i v e c l e a n e r s
should not be used.
C A U T I O N
Do not permit water to get inside controls or shaft
b u s h i n g s . A v o i d t h e u s e o f c h e m i c a l c l e a n i n g
a g e n t s w h i c h m i g h t d a m a g e t h e p l a s t i c s u s e d i n
this instrument. Some chemicals to avoid are ben-
z e n e , t o l u e n e , x y l e n e ,
a c e t o n e o r s i m i l a r c o m -
pounds.
The CRT faceplate, protector plate and filters are as
follows:
Clean the plastic light filters, faceplate protector and the
CRT face with a soft, lint-free cloth dampened with de-
natured alcohol. The CRT mesh filter is easily scratched or
damaged. It should be cleaned as follows:
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.
2. Greasy residues or dried-on dirt are removed with a
solution of warm water and a neutral liquid detergent. Use
the water-color brush to 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 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.
C A U T I O N
D o n o t w r i t e o n t h e C R T f a c e — u s e t h e c l e a n
plastic protector plate mounted in the ornamental
ring.
Lubrication
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
and switch contacts. Lubricate the switch detents with a
heavier grease (Beacon grease No. 325 or equivalent). Do
not over-lubricate. The necessary materials and instructions
for proper lubrication of Tektronix instruments are contained
in a component lubrication kit which may be ordered from
Tektronix. Order Tektronix Part No. 003-0342-00.
The dial and tuning assembly should be lubricated period-
ically. This is normally every 500 hrs., however if the tuning
tends to bind or drag it may be due to improper lubrication.
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