f. Remove the four cover screws.
g. Remove the cover, The fixed oscilltor com-
Q552 (9) are accessible for replacement.
NOTE
Closely observe the position of compon-
ents and their lead lengths. Replace
components as closely as possible to
their original position.
h. To gain access to mixer components, the
printed circuit assembly must be removed
from the enclosure.
i. Unsolder capacitor
C555 (20) and resistor
R558 (19) from filter FL551.
j. Unsolder capacitor
C554 (28) from connec-
tor J551.
k. Remove the six panhead screws which se-
cure the mounting bracket (3) to the enclosure.
l. Carefully withdraw the mounting bracket
and mixer printed circuit board assembly from
the enclosure.
m. The mixer components are accessible for
removal and replacement.
n. Remove and replace mixer diodes CR-
551 (26), CR552 (24), CR553 (22), and CR554
(21) if required. Remove and replace other com-
ponents if required.
NOTE
Observe the same precautions in restor-
ing the original layout as in other rf
assemblies. When diodes are replaced,
use the correct polarities.
reverse order of disassembly and with the same
care.
e. Disconnect J401 f r o m filter FL551 (16) and
p. Replace the repaired fixed oscillator in the
the AN/USM-203A.
AN/USM-203A assembly.