TM 9-4935-601-14-7&P
Model 8640B
8-19.
Wrench
. A wrench is supplied with the
generator with one end that fits the SMC connectors
used on the generator's RF cables and the other end
that fits another common SMC connector that may be
used in servicing.
8-20.
Spare Fuses and IC Regulator
. The plastic
box mounted on the chassis filter capacitors contains
spare fuses and an IC regulator for the power supply
voltage regulators.
8-21.
Part Location Aids
. The locations of some
chassis-mounted parts and the major assemblies are
shown on the last two foldouts in this manual. The
locations of individual components mounted on printed
circuit boards or other assemblies are shown on the
appropriate schematic diagram page or on the page
opposite it. The part reference designator is the
assembly designator plus the part designator (for
example, A6R9 is R9 on the A6 assembly). For specific
component description and ordering information refer to
the parts list in Section VI.
8-22.
Servicing Aids on Printed Circuit Boards
.
The servicing aids include test points, transistor and
integrated circuit designations, adjustment callouts and
assembly stock numbers.
8-23.
REPAIR
8-24.
Factory Selected Components
8-25.
Some component values are selected at the
time of final checkout at the factory (see Table 5-1).
Usually these values are not extremely critical; they are
selected to provide optimum compatibility with
associated components. These components are
identified on individual schematics by an asterisk (*).
The recommended procedure for replacing a factory-
selected part is as follows:
a. Try the original value, then perform the
calibration test specified for the circuit in the
performance and adjustment sections of this manual.
b. If calibration cannot be accomplished, try the
typical value shown in the parts list and repeat the test.
c. If the test results are still not satisfactory,
substitute various values within the tolerances specified
in Table 5-1 until the desired result is obtained.
8-26.
Etched Circuits
8-27.
The etched circuit boards in the Signal
Generator are of the plated-through type consisting of
metallic conductors bonded to both sides of insulating
material. The metallic conductors are extended through
the component mounting holes by a plating process.
Soldering can be done from either side of the board with
equally good results. Table 8-1 lists recommendations
and precautions pertinent to etched circuit repair work.
a. Avoid unnecessary component substitution; it
can result in damage to the circuit board and/or adjacent
components.
b. Do not use a high-power soldering iron on
etched circuit boards. Excessive heat may lift a
conductor or damage the board.
c. Use a suction device (Table 8-1) or wooden
toothpick to remove solder from component mounting
holes. DO NOT USE A SHARP METAL OBJECT
SUCH AS AN AWL OR TWIST DRILL FOR THIS
PURPOSE. SHARP OBJECTS MAY DAMAGE THE
PLATED-THROUGH CONDUCTOR.
d. After soldering, remove excess flux from the
soldered areas and apply a protective coating to prevent
contamination and corrosion. (Avoid getting flux
remover on the printed circuit board extractors.) See
Table 8-1 for recommendation.
8-28.
Etched Conductor Repair
8-29.
A broken or burned section of conductor can be
repaired by bridging the damaged section with a length
of tinned copper wire. Allow adequate overlay and
remove any varnish from etched conductor before
soldering wire into place.
8-30.
Component Replacement
8-31.
Remove defective component from board.
NOTE
Although not recommended on
boards with high-frequency signals
or where both sides of a board are
accessible, axial lead components,
such as resistors and tubular
capacitors, can be replaced without
unsoldering. Clip leads near body of
defective component, remove
component and straighten leads left
in board. Wrap leads of replacement
component one turn around original
leads. Solder wrapped connection
and clip off excess lead.
8-3
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com