
TM 9-4935-601-14-7&P
Model 8640B
CHANGE 29 (cont'd)
Service Sheet 16 (Principles of Operation):
Under
Meter Attenuator and Odd Range Code (A1)
delete the fourth sentence.
Service Sheet 16 (schematic):
Delete resistors A1A1R5 and R6 and associated wiring.
On switch A1SlBF/R, connect switch terminals 7 and 9 to terminal 6.
CHANGE 30
Page 6-14, Table 6-3.
Add: A8A2C27, 0140-0205, CAPACITOR-FXD 62 PF+5% 300WVDC MICA
Page 6-15, Table 6-3
Change A8A2U6 and U25 to 1820-1322, IC-SN74S02N, GATE
Service Sheet 20 (schematic)
Add: C27, 62 pF between A8A2U13D pin 11 and ground.
Change A8A2U6 and U25 to 1820-1322.
CHANGE 31
Page 6-23, Table 6-3:
Change A1OA2U1 to 1826-0303 IC, LINEAR.
Service Sheet 11 (schematic):
Change part number for A1OA2U1 to 1826-0303.
CHANGE 32
Page 5-3, Table 5-1:
Delete AllR28 (Option 001).
Pages 5-9 and 5-11, paragraph 5-27:
Under EQUIPMENT, add the following instruments.
Distortion Analyzer ..............................................................................................
HP 333A
Oscilloscope ........................................................................................................
HP 180A/1801A/1820C
Change step 12 to read as follows:
12.
If level at A11TP4 is too high, adjust AllR28 ccw (reduce resistance); if level is too low, adjust AllR28
cw (increase resistance). Then repeat steps 8 through 11.
Add the following steps after step 16.
16a.
Set MODULATION FREQUENCY controls to 600 kHz. Connect distortion analyzer to front panel AM OUTPUT
connector. Calibrate distortion analyzer and measure distortion. Distortion analyzer should indicate less than
2%.
16b.
Set MODULATION FREQUENCY controls to 20 Hz. Connect oscilloscope to AM OUTPUT connector. Set AM
switch alternately between OFF and INT. The envelope of the audio signal displayed on the oscilloscope should
stabilize within a few seconds after AM is switched to INT.
16c.
If distortion or AM stability is incorrect, adjust A11R28 ccw (reduce resistance) for less distortion or cw (increase
resistance) for better stability.
NOTE
Adjustment is correct when distortion and stability are as described in steps 16a and 16b.
Measurement results recorded in preceding steps may have changed (perhaps beyond stated
limits) after readjusting A11R28.
7-74
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