Fig. 6-33. Adjusting avalanche voltage.
just below the state of free running avalanche. Free running
avalanche, appears as an RF burst signal between the 1 MHz
pulses as shown in Fig. 6-33C; or with the INT REF FREQ
control in the OFF position, the free running avalanche
transistor signal will feed through to the 1 MHz MARKERS
OUT connector, and appear on the test oscilloscope as a
2 MHz burst. If free running avalanche does not occur, turn
the adjustment fully clockwise.
F i g . 6 - 3 4 . L o c a t i o n o f L 1 1 0 4 a n d 1 1 1 0 8 , R 1 1 5 0 a n d R 1 1 4 0 .
e. Switch the band selector to band C. Turn the INT REF
FREQ control on.
f. Push the LOCK CHECK button. Check for beat signal
displays as the FINE RF CENTER FREQ control is rotated
through its range.
27. Adjust 1 MHz REF FREQ Range
o
a. Equipment set up is given in step 26.
b . A p p l y t h e o u t p u t f r o m t h e 1 M H z M A R K E R S O U T
signal through a
10×
attenuator to J120 on the honeycomb
assembly as follows: Connect a GR to Sealectro adapter
(such as a P6040 probe cable), a GR to BNC adapter and a
20 dB attenuator, (see Fig. 6-32) between the 1 MHz MARK-
ERS OUT connector and J120. Disconnect the Sealectro
connector from J120.
c. Set the DISPERSION to 100 kHz/Div and position a
1 MHz marker to the screen center with the IF CENTER
FREQ control.
d. Adjust L1108 (Fig. 6-34) for a positive oscillator start
when the INT REF FREQ control is turned from its OFF to
ON position. The signal position on the screen should be
consistent as the INT REF FREQ control is switched from
OFF to the initial ON position. (The control must not be
turned past the initial ON position or the oscillator frequency
will be changed.]
e. Rotate the INT REF FREQ control through its range
Check the total frequency shift of the internal reference
1 MHz marker.
6-30
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 ...