
Model 8640B
TM 9-4935-601-14-7&P
A26 Assembly and Disassembly
SERVICE SHEET E
SERVICE SHEET F
General Removal Procedures
Top and Bottom Cover Removal
CAUTION
Before attempting to disassemble or remove any part of the generator, remove line power from the instrument by disconnecting the
instrument's line power cable from the line power outlet.
1. Remove top cover by removing four screws. Slide cover to the rear approximately two inches to disengage it from flanges at the instrument's front and rear.
Lift it off.
2. Remove bottom cover by removing four screws. Slide cover to the rear approximately two inches to disengage it from flanges at the instruments front and
rear. Lift it off.
Circuit Board Removal
3. Remove any plug-in circuit board by gently lifting the board's extractors (the extractors are color-keyed to the guides at the board's edges).
M1 Removal
1. Remove top cover.
2. Remove trim strip (extrusion ) that overlaps panel meter by removing two flat-head screws. Remove plastic front panel window by lifting it up and out.
3. Remove A4 Meter/Annunciator Drive Assembly.
4. Remove four pan-head screws (with lockwashers) that secure A8 Counter/Lock Assembly to chassis.
5. Remove A6 Annunciator Assembly by first disconnecting plug A6P1 and removing two flat-head screws on front face of meter bezel. Then lift left edge of A8
Assembly and move A6 Assembly to the rear.
6. To remove meter, disconnect two wires at rear of meter (black-wire from negative post, white wire to positive post).
7. Push top edge of meter to the rear and lift meter from chassis.
NOTE
If necessary, loosen All Modulation Oscillator to provide clearance for meter (see Service Sheet C).
8. To install meter, reverse procedure given in steps one through seven. To install Annunciator Assembly, reverse procedure given in steps one through five.
NOTE
Check that the insulator between the right-hand annunciators and the counter is properly in place to prevent shorting of the lamps.
A3 Removal
1. Place instrument upside down and remove bottom cover.
CAUTION
While working with and around the semi-rigid coaxial cables in the generator, do not bend the cables more than necessary. Do not torque
the RF connectors to more than 2 inch-pounds.
2. Remove FREQUENCY TUNE and FINE TUNE knobs from front panel. The knobs are secured to shafts with allen screws in the knobs.
3. Disconnect two semi-rigid coaxial cables at rear of A3 RF Oscillator Assembly (cable W2 at A3A1A3J1 and cable W3 at A3A1A2J1).
4. Remove two nuts (with lockwashers) that secure the A3A4 Connector Board Assembly to the chassis (located at the rear of the A10 Divider/Filter Assembly
casting). Remove the A3A4 Assembly from its socket.
CAUTION
Do not apply rotational torque to the Oscillator Assembly or it may loosen and cause RFI leakage and uncalibration.
5. Remove four pan-head screws (with lockwashers) that secure the A3 Assembly to chassis. Remove assembly by lifting free of the four standoffs and sliding
it to the rear and up.
6. Reinstall assembly by reversing procedure in steps one through five.
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