Fig. 4-16. Removing the phase-lock assembly board.
1. Band A Mixer Diodes
a. Disconnect the sub-miniature connectors, remove the
two mounting screws and the mixer assembly.
C A U T I O N
D o n o t t i p o r b e n d t h e c o n n e c t o r s i n r e m o v i n g
t h e m . G r a s p t h e b o d y o f t h e c o n n e c t o r w i t h t h e
f i n g e r s o r n e e d l e n o s e p l i e r s a t t h e b a s e o f t h e
connector, and pull straight out.
b. Remove the four screws and spacers that hold the
cover and circuit plate to the shell.
c. Unsolder and replace the diodes with a matched pair.
S e e F i g . 4 - 1 8 A . U S E A H E A T S I N K W H E N S O L D E R I N G
T H E N E W D I O D E S I N T O P L A C E , S E E S O L D E R I N G T E C H -
N I Q U E .
e. Replace the cover and the mixer assembly. Reconnect
the connectors to the mixer assembly.
2. Band B Mixer Diode
a. Remove the front panel mounting nut and washer.
b. Slip the mixer assembly back and out of the unit.
c.
Unscrew the front barrel (1 dB pad) and replace the
mixer diode. See Fig. 4-18B.
3. Band C Mixer Diodes
a. Coaxial Mixer. Unscrew the base of the coaxial mixer.
Fig. 4-18C. Replace the diode and re-assemble the mixer.
b. Waveguide Mixers. Unscrew the cap over diode and
replace the-diode. See Fig. 4-18D.
Oscillator Tube Replacement
N O T E
A c o m p l e t e o s c i l l a t o r a s s e m b l y
a n d i t s s u b p a r t s
are listed in the Mechanical Parts section. Replac-
ing components such as the oscillator tubes requires
a c o m p l e t e r e c a l i b r a t i o n w i t h s p e c i a l t e s t e q u i p -
m e n t a n d t e c h n i q u e . W e t h e r e f o r e r e c o m m e n d
replacing the complete assembly and returning the
d e f e c t i v e a s s e m b l y t o y o u r T e k t r o n i x F i e l d o f f i c e
o r r e p r e s e n t a t i v e . A c a l i b r a t i o n p r o c e d u r e i s p r o -
vided in the Calibration section, if it is impractical
t o r e t u r n t h e a s s e m b l y f o r r e p a i r .
The oscillator tube should only be replace after all tests
indicate the tube is faulty. Check supply voltages, etc., as
illustrated in Fig. 4-19A.
1. Band A and B oscillator tube replacement (V40 and V41)
a. Unscrew and remove the screws that hold the tap plate
to the oscillator chamber. Remove the top plate.
4-13
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 ...