Model 8640B TM 9-4935-601-14-7&P
CHANGE 25
Page 5-2, paragraph 5-21:
Change paragraph e to read as follows:
e. A9A1A2C6, C7 and C8. If the A9A1A2 FM Gain Switch Board Assembly has been replaced or repaired,
measure the 3 dB bandwidth at A7TP3 with an oscilloscope on the following RF frequency ranges while
driving the FM INPUT connector with an external test oscillator. Change the corresponding capacitor, if
necessary, for best flatness (less than 3 dB down at 250 kHz rate). Increase capacitance to decrease
deviation (250 kHz rate).
FREQUENCY PEAK DEVIATION
RANGE (MHz) Range Capacitor
512 - 1024 5 kHz A9A1A2C8
256 - 512 5 kHz A9A1A2C7
128- 256 5 kHz A9A1A2C6
NOTE
Changing any capacitor will likely affect flatness on other ranges.
Page 5-2, Table 5-1:
Delete A9C8 (see Change 1).
Add the following:
Service Range of Basis of Selection
Component Sheet Values
A9A1A2C6 6 0 - 56 pF
A9A1A2C7 6 500 - 900 pF See paragraph 5-21
A9A1A2C8 6 750 - 2000 pF
Page 6-17 and 6-18, Table 6-3:
Replace the entire A9 assembly parts list with the following list.
A9 ---------------- PEAK DEVIATION AND RANGE SWITCH ASSEMBLY
A9A1 08640-60179 SWITCH ASSEMBLY
A9A1MP1 0380-0013 SPACER, 1.0 LONG
A9A1MP2 0380-0013 SPACER, 1.0 LONG
A9A1MP3 0510-0005 RING, RETAINER 1/4 DIA
A9A1MP4 0510-0005 RING, RETAINER 1/4 DIA
A9A1MP5 0510-0005 RING, RETAINER 1/4 DIA
A9A1MP6 0510-0015 RING, RETAINER EXT
A9A1MP7 0510-0052 RING, EXT 0.125 DIA
A9A1MP8 0510-0052 RING, EXT 0.125 DIA
A9A1MP9 1430-0759 GEAR, SPUR
A9A1MP10 1430-0772 GEAR, PLANET
A9A1MP11 1430-0772 GEAR, PLANET
A9A1MP12 1430-0773 GEAR, COMBINATION
A9A1MP13 1430-0774 GEAR, COMBINATION
A9A1MP14 1460-0019 SPRING, COMPRESSION
7-56
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