Section III and IV
leads and detector output leads are brought out of the
is contained in an aluminum shield which is insulated
r-f unit through a filter assembly consisting of five
from the panel and audio chassis as well as from the
sections; four of these are in use, one is a spare.
r-f chassis within which it is contained. This insula-
This filtering is required to prevent radiation from
tion is necessary to minimize r-f leakage and is
the unit on the external leads.
broken only at a few carefully selected points. Power
SECTION IV
PERIODIC INSPECTION AND MINOR REPLACEMENT AND REPAIR
c. Connect a cathode ray oscilloscope to the AUDIO
4-1. PERIODIC INSPECTIONS.
OUT connector.
Make the
4-2. PRE - OPERATION INSPECTION.
d. Set the AUDIO SELECTOR switch to each of its
following check on Signal Generator SG-13/ARN im-
settings and check the wave forms obtained per para-
mediately preceding each operation period.
graphs 6-10 through 6-18. Excess ive distortion may
be an indication of a defective tube or component in the
a. Turn SET LINE TO 21V control to OFF position
audio section. Noise or ripple on the wave forms is
and check mechanical zero of meter with SG-13/ARN
often an indication of defective dynamotor operation.
in normal operating position.
See Section VI, paragraph 6-20.
b. Connect Power Cord CX-1095/U or CX-1506/U
4-5. VOR ACCURACY CHECK.
to the 2 lVDC-29VDC connector on SG-13/ARN and to
the 21-29 volt source of power.
a. Connect the SG-13/ARN through a 6-db, 53-ohm
attenuator pad to an ARN-14 navigation receiver
c. Turn METER switch to LINE position and turn
equipped with omni bearing selector (OBS) and a pre-
SET LINE TO 21V switch until the meter reads 21
cision crosspointer meter. Set the frequency of the
0.5 volts.
signal generator and receiver to 114.9 mc. Set NAV-
GS switch to NAV. Allow SG-13/ARN to warm up at
d. Turn METER switch to B+ position and read B+
least 15 minutes and adjust SET LINE TO 21V control
voltage on meter. Reading should be 230 volts. Allow
for 21V 0.5V on panel meter. Set METER ZERO and
3 minutes warm up.
adjust carrier level to red line. See figure 8-5, part
2 for connections.
e. With METER switch in CAR position and
CARRIER SET control fully counterclockwise adjust
b. Set the SG-13/ARN AUDIO SELECTOR on VOR,
METER ZERO control until the meter reads zero.
the VOR switch to 0, and the MICROVOLTS dial to
1000.
f. Rotate MICROVOLTS dial to 200, 000 microvolt
and set the METER switch in the CAR position. At
c. Adjust the SET control on Indicator ID-249A until
each MEGACYCLES dial setting at which the SG-13/
the crosspointer is centered at the setting of approxi-
ARN is to be used set meter to red line with CARRIER
mately 0 and the TO-FROM indicator reads TO.
SET control. If the meter cannot be set to the red
line, faulty operation of the r-f section is indicated.
d. Disconnect the SG-l3/ARN and substitute a modu-
Refer to Section VI, Trouble Shooting and Correction
lator MD-83/ARN modulating an SG-l/ARN signal
for corrective procedure.
generator with a standard VOR signal. Use the same
6-db pad at the receiver input. See figure 8-5, part
4-3. INTERMEDIATE INSPECTION (not to exceed
1 for connections.
100 hours).
e. Set the SG -1 /ARN microvolt dial to 500. Vary
4-4. OVERALL OPERATIONAL CHECK .
the MD-83A/ARN VOR dial setting until the cross-
pointer is again centered with the TO-FROM indicator
a. Perform Pre-Operation Inspection, checking to
reading TO.
see if the unit can be red lined at each megacycle step
from 135.5 down to 108.5.
f. Subtract the SG-13/ARN VOR switch setting from
the MD-83A/ARN VOR dial setting to obtain the VOR
b. At 108 MC check operation of all fine frequency
error.
oscillator crystals by rotating the tenth-megacycle
selector of the MEGACYCLES control through all 10
g. Repeat steps a through f for each setting of the
positions and observing if the unit can be red lined at
SG-13/ARN VOR switch. VOR error should not ex-
each setting.
ceed 0. 7 degree at any setting of the VOR switch.
18
