
TM 9-4935-601-14-7&P
Model 8640B
A1 Assembly Removal and Disassembly
SERVICE SHEET A
SERVICE SHEET B
A8 Assembly Removal and Disassembly Procedure
A8 Casting Cover Removal
1. Place instrument right side up and remove top cover
(see Service Sheet F).
2. Remove trim strip (extrusion) that overlaps front of A8
Assembly casting by removing two flat-head screws.
Remove plastic front panel window by lifting it up and
out.
3. Remove three pan-head screws on front of casting and
remove the button shield. Remove eight pan-head
screws (with lockwashers) that secure casting cover to
casting (screws marked with asterisk * - on casting
cover).
4. Lift cover from two "honey comb" RF shields and
casting.
A8A2 and A8A4 Removal
5. Remove two pan-head screws (with lockwashers) that
secure the A8A2 Assembly. Remove A8A2
Counter/Lock Board Assembly and A8A5 Riser
Assembly by lifting at the riser; the A8A4 Counter
Display Assembly is attached to the A8A2 Assembly do
not damage the brass LED/button shield while removing
the assemblies.
NOTE
The A8A2 and A8A4 Assemblies can be
extended for service by removing the A8A5
Riser Assembly from A8A2 and installing
A8A2 on the extender board in the riser
socket (A8A3XA8A5). This also gives access
to the A8A3 Time Base Assembly.
CAUTION
Do not remove A8A4 from A8A2 unless
necessary. If it has been removed, exercise
care during reassembly to avoid bending the
connector pins and sockets.
A8A1 Access
WARNING
The edges of the RFI gasket may be sharp
and may cause personal injury if not
handled with care.
6. To gain access to the A8A1 RF Scaler Assembly,
remove six pan-head screws (with lockwashers) that
secure the cover shield. Remove the cover shield and
gasket.
A8 Removal
NOTE
The entire A8 Assembly must be removed
from the chassis to remove the A8A1 and
A8A3 Assemblies.
Do not attempt to replace components on
the A8A1 and A8A3 Assemblies (except
A8A1U3) without removing the boards.
7. Turn instrument upside down and remove bottom cover
(see Service Sheet F).
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.
8. Disconnect two semi-rigid coaxial cables from bottom of
A8 Assembly (cable W2 at A8A1J2 and cable W14 at
A8A1J1). Disconnect green flexible coaxial cable from
bottom of A8 Assembly (cable W15 at A8A3J1).
9. Turn instrument right side up. Remove A8 Assembly by
removing four pan-head screws (with lockwashers) that
secure the A8 Assembly to the chassis.
A8A1 Removal
10. Remove two pan-head screws that secure A8A1U3;
remove two lockwashers, two washers, and two nylon
bushings. Remove A8A1U3 and two mica washers.
11. On bottom of A8 Assembly casting, under A8A1
Assembly, remove hex nut and lockwasher. Remove
two hex nuts and lockwashers that secure coaxial
connectors A8A1J1 and J2.
8-72
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