
Model 8640B
TM 9-4935-601-14-7&P
A8 Assembly Removal and Disassembly
SERVICE SHEET B
SERVICE SHEET C
A9 Assembly Removal Procedure
1. Set PEAK DEVIATION and RANGE switches fully counterclockwise.
2. Remove PEAK DEVIATION and RANGE switch knobs. The knobs
are secured to their shafts with allen screws in the knobs.
3. Place instrument upside down and remove bottom cover (see Service
Sheet F).
4. Loosen coupling between RANGE switch shaft and A10 Divider/Filter
Assembly.
5. Remove two nuts and lockwashers that secure A9 Assembly to front
panel (located at switch bushings).
6. Remove connector A9P1 from jack on A13 Assembly. Lift out A9
Assembly.
7. Reinstall assembly by setting both switch shafts fully counterclockwise
and reversing the procedures in steps one through six.
NOTES
1. The detents of both the A9 Assembly and A10
Assembly switches must align and correspond to the
same positions. Check that the actual RF output
frequency agrees with the counter indication on all
bands.
2. Adjust the coupler longitudinally for minimum binding
and tighten the setscrews very securely.
A11 Assembly Removal Procedure
A11 Removal (Standard)
1. Remove bottom cover from instrument (see Service Sheet F).
2. Set MODULATION FREQUENCY knob to 400 Hz. Remove
MODULATION FREQUENCY knob. The knob is secured to its shaft
with allen screws.
3. Remove A11 Assembly by gently lifting the board extractor at rear of
board and sliding assembly to the rear and out of chassis.
4. To connect A11 Assembly for service, place assembly on extender
board and install in chassis. Reinstall MODULATION FREQUENCY
knob with 400 Hz position toward top of instrument.
A11 Removal (Option 001)
1. Remove top and bottom covers from instrument (see Service Sheet
F).
2. Set MODULATION FREUQENCY knob to 400 Hz (fixed). Remove
MODULATION FREQUENCY knob, vernier knob, and cursor disc and
gear. The knobs are secured to concentric shafts with allen screws in
the knobs.
CAUTION
When removing cursor disc and gear, gently slide it off
the shaft to avoid damage to the disc.
3. Remove pan-head screw (with washer and lockwasher) that secures
A11 Assembly to A13 Mother Board Assembly. The screw is
accessible from top of instrument.
4. Remove A11 Assembly by gently lifting the board extractor at rear of
board and sliding assembly to rear and out of chassis.
5. To connect A11 Assembly for service, place assembly on extender
board and install in chassis. Reinstall cursor disc and gear,
MODULATION FREQUENCY knob, and vernier knob. 400 Hz
position of knob should be toward top of instrument.
A11 Reinstallation
6. Reinstall A11 Assembly by reversing the procedures in steps one
through four or five.
NOTE
Check variable frequency accuracy to assure that the
vernier disc is in the proper position.
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