TM 11-6625-1633-45
CHAPTER 4
REPAIRS AND ADJUSTMENTS
Section I. REPAIRS
To remove the rf oscillator section, proceed as follows:
4-1. General Parts
Replacement
Tec h-
niques
a. Disconnect plug P8 and coaxial connectors P14,
A4P1, and A4P2.
NOTE
reached and replaced easily without special procedures.
Coaxial connectors A4P1 and A4P2 are
The tube sockets, capacitors, filter chokes, and inductors
connected to coaxial relay K4 which is
are mounted securely to the chassis with hexagonal nuts
mounted on the front panel.
or binding head screws.
b. Rotate the ATTENUATOR control knob for an
indication of approximately -80 dbm (to provide clear-
The nuts securing the transformers can easily be re-
ance for gear train components).
moved with a socket wrench. The dial knobs are re-
c. Remove the four hexagonal screws located at each
moved with Allen wrenches. The thermistor covers are
rf oscillator section support.
removed by loosening the two screws on the cover plate.
d. Push the rf oscillator section far enough forward
c. If any of the wafer switches or potentiometers re-
so that it may be grasped from the front.
quire replacement, carefully tag the wires or sketch the
e. Pull the rf section away from the front panel.
connections to avoid misconnection when the new com-
ponent is installed. Follow this practice whenever re-
NOTE
placement requires the disconnection of numerous wires.
Do not allow the attenuator-probe cables
to be crushed against the frame of the
d. Be very careful when replacing transistors in the
main chassis during removal.
AN/URM-149. Use a pencil-type soldering iron with a
25-watt maximum capacity. Some circuits of the signal
f. Replace the rf oscillator section by sliding the rf
oscillator section on to its supports in the main chassis.
be connected to an ac power source, use an isolating
power transformer between the iron and the ac power
g. Insert the four screws through each support and
line. Do not use a soldering gun; it may induce damag-
the rf oscillator section.
ing voltages in components.
h. Connect plug P8 and coaxial connectors, P14,
AlP1, and A1P4.
Where wiring permits, use a heat sink (such as long-
nose pliers) between the soldered joint and the transis-
NOTE
tor. Use approximately the same length and dress of
The tracking subassembly must be re-
transistor leads as used originally. For additional tech-
moved from the rf oscillator section chas-
niques of soldering refer to TB SIG 222.
sis to replace most of its components or
tracking potentiometer A4R20 or A4R23.
When a tracking adjustment potentiome-
4-2. Removal and Replacement of RF O s-
ter of fixed resistor is replaced, perform
cillator Section
the alignment procedures given in para-
graph 4-18.
The rf oscillator section is mounted on the right side of
the main chassis as shown in figure 3-10.
i. When the rf oscillator section is removed (a
4-1
