TM 11-6625-2631-14
6-5. Alignment
1.0 scale division on the test set meter. Install
resistor.
The test set requires no alignment. Tolerances
(5) Disconnect test equipment.
allowed for individual load resistors are sufficient to
permit slight variations in resistive values and still
keep the test set within specifications.
Figure 6-1 is an exploded view of the test set with
6-6. Repair
all components identified on the associated legend.
Careless replacement of parts often creates new
board. External test set components are identified
f a u l t s . Observe good workmanship at all times.
on figure 1-1. T o gain access to internal com-
When performing repairs by replacement of parts,
ponents, or to remove the meter or test connectors,
follow the general techniques and cautions given in
t h e unit must be disassembled. The following
the following paragraphs.
paragraphs provide a brief description of the steps
a. Before a part is unsoldered, note the position
required for disassembling the test set to gain access
of the leads. If the part to be replaced has a number
t o and to remove the terminal board and com-
of connections, tag each of the leads.
p o n e n t parts.
b. Be careful not to damage other leads by
a . U n i t D i s a s s e m b l y a n d R e a s s e m b l y (fig. 6-1).
pulling or pushing them out of the way.
(1) Remove six screws (23) from the bottom
c. Do not allow drops of solder to fall into the
chassis (13) and carefully slide the cover section
equipment; they may cause short circuits.
(21) from the chassis.
d. M a k e w e l l - s o l d e r e d j o i n t s ; a c a r e l e s s l y
( 2 ) Reassemble by replacing the cover section
soldered joint may create a new fault, and a poorly
(2) over the chassis (13) and replace the six screws
soldered joint is one of the most difficult faults to
(23) removed in step (1).
find.
b. Battery Data and Instruction Cards. T h e
battery data and instruction cards (3 through 8) are
s o l d e r i n g small components or semi-conductor
retained within the compartment on the rear of the
devices. Excessive heat may damage the component
unit by two screws (25) and a spring clip (26). If
or change its value.
cards are to be replaced, remove the two screws,
f. When a part is replaced, it must be positioned
s l i d e out and replace the particular card. The
exactly as the original part. A defective part may be
spring does not have to be removed. Replace the
replaced with one which has the same electrical
two screws after the cards are inserted.
value but a different physical size, if space permits.
c. Circuit Board Removal and Replacement (fig.
Pay particular attention to proper grounding when
6-1). The circuit board, figure 6-2 (24 fig. 6-1). is
replacing a part. Use the same ground as a original
secured to the test set case by "pop" rivets, as are
wiring. Failure to observe these precautions may
other components within the unit. In each case.
result in intermittent operation.
when a respective component is to be removed from
g. When replacing parts which have factory-
the unit, the "pop" rivets must be drilled out with a
s e l e c t e d values, use replacements which have a
l/8-inch drill bit. When the component is replaced.
v a l u e equal to that of the part removed. The
it is optional whether "pop" rivets are again used
selection is originally made by slightly varying the
for attachment, or whether MS hardware is used
v a l u e of the part until the desired operation is
instead. To remove the circuit board, proceed as
obtained. Factory-selected parts are indicated on
follows:
the schematic diagram. A choice of four values of
(11) Unsolder and tag leads to circuit board
resistor R1 is available as indicated in appendix C.
(24).
Use the AN / USM-223 and PP-3940 / G to select
( 2 ) Drill out "pop" r i v e t s (16) and spacers
resistor R1 (6040, 6190, 6490, or 6810 ohms) as
(15) which secure the circuit board to the cover.
follows:
(3) To replace the circuit board (24), solder
(1) Set power supply output to zero.
the leads removed in step (11) and replace the at-
(2) Connect power supply positive and
taching hardware with either rivets or screws, lock
negative outputs to pins A and B. respectively. of
w a h e r s , and nuts (3 each).
the URC-1 cable connector.
d. Connector
Block
Removal
(3) Connect multimeter across power supply
and
Replacement. The connector block (19. fig. 6-1) is
output and adjust power supply for 15.7 volts.
also secured by "pop" rivets (17). Follow the same
(4) Select the replacement value for resistor
type of removal and
replacement
technique as
R 1 from one of the resistors listed above. The
described for the circuit board (c above).
correct replacement will provide a scale reading of
