The gears should be lubricated with a high quality lubri-
c a n t s u c h a s C O S M O L U B E N o . 1 0 2 , ( T e k t r o n i x P a r t N o .
006-1229-00). The bearing surfaces and drive shaft should be
oiled with a light weight oil such as Hoppes lubricating oil
or Pfaff sewing machine oil.
Lay the instrument on its side. Using a syringe or hypoder-
mic oiler (Tektronix Part No. 003-0280-00) and apply no more
than one drop to each point. The gear shafts that are below
t h e R F C E N T E R F R E Q U E N C Y a n d o s c i l l a t o r t u n i n g s h a f t s
can be reached with the hypodermic oiler, or a small wire
which will wick the oil to the out-of-the-way points. Do not
apply oil to the tuning shaft from the front panel of the
instrument.
The lead screw (long threaded shaft) that tunes the C band
oscillator cavity should not require lubrication.
It should,
however, be cleaned with a soft brush and mild detergent
solution.
Visual Inspection
After a thorough cleaning, the instrument should be care-
fully inspected for such defects as poor connections, dam-
aged ports and improperly seated transistors. The remedy
for most visible defects is obvious; however, if heat-damaged
parts are discovered, determine the cause of over-heating
before the damaged parts are replaced, otherwise the dam-
age may be repeated.
Transistor Checks
Periodic preventive maintenance checks consisting of re-
moving transistors from the instrument and testing them in
a tester, are not recommended. The circuits within the instru-
ment provide the only satisfactory check on transistor per-
formance. Defective transistors are usually detected during
recalibration of the instrument. Details of in-circuit transistor
checks are given in the troubleshooting procedure in this
section.
Performance Checks and Recalibration
To insure accurate measurements, the instrument per-
formance should be checked after each 500 hours of opera-
tion or every six months if the instrument is used intermittent-
ly. The calibration procedure is helpful, both in the isola-
tion of major troubles in the instument, and in locating
minor troubles which are not apparent during regular oper-
ation. Instruction on how to conduct a performance check
are given in Section 5, Calibration instructions are described
in Section 6.
C O R R E C T I V E M A I N T E N A N C E
Corrective maintenance consists of component replacement
and instrument repair. Special techniques or procedures
required to replace components in this instrument are de-
scribed in this section.
N O T E
Maintenance and repair of the RF Local Oscillator,
Mixer and Filter sections should not be attempted.
T h e o s c i l l a t o r t u b e s a n d m i x e r d i o d e s c a n b e
4 - 2
r e p l a c e d p r o v i d e d r e a s o n a b l e c a r e i s u s e d , a n d
their replacement is performed by competent per-
s o n n e l . ( S e e r e p l a c e m e n t i n s t r u c t i o n s i n t h i s s e c -
tion.) Circuit components have been selected and
positioned at the factory using special test equip-
ment. Tracking adjustments for the local oscillator
s e c t i o n r e q u i r e s p e c i a l t e s t e q u i p m e n t a n d t o o l s .
Obtaining
Replacement Parts
Before purchasing or ordering replacement parts, con-
sult the Parts List for value, tolerance and rating. The Parts
sections contain instructions on how to order replacement
parts from Tektronix.
N O T E
W h e n s e l e c t i n g t h e r e p l a c e m e n t p a r t s , i t i s i m -
p o r t a n t t o r e m e m b e r t h a t t h e p h y s i c a l s i z e a n d
s h a p e o f t h e c o m p o n e n t m a y a f f e c t i t s p e r f o r m -
ance in the circuit.
Component Numbering and Identification
The circuit number of each electrical part is shown on
the circuit diagrams. A functional group of circuits (such
T A B L E 4 - 1
Summary of Contents for 491
Page 4: ...i i Fig 1 1 The Type 491 Spectrum Analyzer ...
Page 24: ...2 16 Fig 2 17 Control set up chart ...
Page 34: ...Fig 3 1 Function block diagram of the Type 491 3 2 ...
Page 42: ...Fig 3 10 Block diagram of the video detector and vertical amplifier 3 1 0 ...
Page 48: ......
Page 53: ...Fig 4 4 Power Supply Circuit board assembly with wiring color code 4 5 ...
Page 54: ...Fig 4 5 Horizontal Display circuit board assembly showing color code to pin connectors 4 6 ...
Page 55: ...Fig 4 6 IF Control board assembly Wiring color code to pin connector 4 7 ...
Page 64: ...Fig 4 20A Tube subassembly removal procedure 4 16 ...
Page 65: ...Fig 4 20B Tube subassembly installation procedure 4 17 ...
Page 68: ...Fig 4 22 Power supply board assembly with component call out 4 2 0 ...
Page 69: ...Fig 4 23 Vertical Amplifier and Blanking board assembly with component call out 4 21 ...
Page 70: ...Fig 4 24 IF control board assembly with component call out 4 22 ...
Page 71: ...Fig 4 24 IF control board assembly with component call out 4 23 ...
Page 72: ...Fig 4 25 Horizontal display board with component call out 4 24 ...
Page 73: ...Fig 4 25 Horizontal display board with component call out 4 25 ...
Page 74: ...Fig 4 26 Phase lock board with component call out 4 26 ...
Page 88: ......
Page 90: ...Fig 6 1 Test equipment recommended for calibration of the Type 491 6 2 ...
Page 138: ......
Page 192: ......
Page 195: ...SECTION II B 3 ...
Page 196: ......
Page 200: ......
Page 201: ...SECTION 9 DIAGRAMS MECHANICAL PARTS LIST ILLUSTRATIONS ACCESSORIES ...
Page 202: ......
Page 203: ...9 1 ...
Page 204: ...9 3 ...
Page 205: ...9 5 ...
Page 206: ...9 7 ...
Page 207: ...9 9 ...
Page 208: ...9 11 ...
Page 209: ...9 13 ...
Page 210: ...9 15 ...
Page 211: ...9 17 ...
Page 212: ...9 19 ...
Page 213: ...9 21 ...
Page 214: ...9 23 ...
Page 215: ...9 25 ...
Page 216: ...9 27 ...
Page 217: ...FIG 1 9 29 ...
Page 218: ...FIG 2 REAR 9 31 ...
Page 219: ...9 33 FIG 3 IF CHASSIS PHASE LOCK ASSEMBLIES ...
Page 220: ...FIG 4 POWER CHASSIS 9 35 ...
Page 221: ...FIG 5 TIME DIV SWITCH OSCILLATOR ASSEMBLIES 9 37 ...
Page 222: ...FIG 6 CRT SHIELD ASSEMBLY 9 39 ...
Page 223: ...FIG 7 CABINET ASSEMBLY HANDLE 9 4 1 ...
Page 224: ...FIG 8 491 STANDARD ACCESSORIES FIG 8 491 STANDARD ACCESSORIES 9 43 ...
Page 225: ......
Page 226: ...PIN 028017 000 ...