(h)  
Frequency selection is accomplished with the use of the frequency selector knobs on the ADF control panel. BCD (binary coded decimal) information is fed to the frequency synthesizer and the band logic circuits. The BCD signals are changed to an incremental voltage and applied to the bandpass filter to change the frequency receiving characteristics.

 (3)  Test Mode
 (a)  
When the self-test switch is energized, a test enable signal is applied to the test generator and the beat frequency oscillator (BFO). The test generator applies a predetermined signal to the goniometer and the sense rf amplifier. The goniometer phasing is unbalanced and causes the receiver to slew to a null position. With a signal applied to the sense rf amplifier, a predetermined sense signal is processed by the ADF receiver. By comparing the loop and sense outputs, a bearing is displayed during self-test to a position defined by the self-test generator signal.

 (b)  
A relay is installed in the ADF receiver which automatically grounds out input RF from the loop antenna when TEST mode is selected at the control panel. This inhibits interference from a strong local transmitting station from entering the loop circuit during TEST mode.

 B. Controls
 (1)  
Prior to operating the ADF system, electrical power must be provided to the airplane (Ref 24-22-00, Electrical Power, Manual Control).

 (2)  
The master radio switches on the P5 pilots' overhead panel and the ADF 1 and ADF 2 circuit breakers (four total) on the P7 electronic circuit breaker must be closed.

 EFFECTIVITY
 AF 121, 122, 152-199;

 IB 406-499;  LH 011-099; SN 303-399;  CONFIG 2 AT, AZ, GN, MD AND VM ALL  09 Page 7
   Sep 25/94

34-57-00

P7 PANEL ADF System Schematic Figure 3 (Sheet 1)
EFFECTIVITYAF 121,122,152-199; IB 406-499;
 CONFIG 2LH 011-099; SN 303-399; 799 Page 8 AT, AZ, GN, MD AND VM ALL Sep 25/94
34-57-00

ADF System Schematic
Figure 3 (Sheet 2)

EFFECTIVITYAF 121,122,152-199; IB 406-499;
CONFIG 2 LH 011-099; SN 303-399; 799 Page 9
34-57-00
AT, AZ, GN, MD AND VM ALL Sep 25/94
 (3)  For each ADF system, when the function switch is positioned to ADF and the receiver is tuned to receive a radio station, the appropriate ADF needle in each RMI should point toward the received station, confirming that the system is operating properly. Ground bearing checks may be adversely affected inside hangers, by large metallic objects in the vicinity, interferring terrain, and weak signals from transmitting stations.
 EFFECTIVITY
 AF 121, 122, 152-199;

 IB 406-499;  LH 011-099; SN 303-399;  CONFIG 2 AT, AZ, GN, MD AND VM ALL  02 Page 10
   Sep 25/94

34-57-00
 ADF SYSTEM - TROUBLE SHOOTING
_____________________________
 1.  General
_______
 A.  The following trouble shooting procedures are based on performance of the system operational test and are presented in tree-type format. The test steps (heavy-line box) are connected by shaded arrows to show the OK condition path. When all steps in the OK condition path check out, the system is operable.
 B.  When a test step does not check out, follow the NOT OK line to the box containing the trouble symptom. Turn to the procedure indicated and continue to follow a single line by analyzing the results of each test step until the required corrective action is determined. Perform the specified correction action, then repeat the step at which the failure was encountered.
 C.  All trouble shooting procedures are based on the assumption that wiring is OK, that electrical power is available and that interphone and MHRS are operational. If the corrective action in the procedures does not correct the problem, check wiring using the wiring diagram.
 D.  The trouble shooting procedures are for either ADF system No. 1 (captain's) or ADF system No. 2 (first officer's). If a component is to be replaced, it could be interchanged with the other system counterpart to confirm the diagnosis.
 NOTE: Poor, noisy reception can result from painting sense antenna with
____
 wrong paint.

 2.  Prepare for Trouble Shooting
____________________________
 A.  Provide electrical power (Ref 24-22-00, Manual Control - Maintenance Practices [Apply Power]).
 B.  Verify that all ADF and INTERPHONE circuit breakers on P7 panel and control stand are closed.
 C.  Set mode selector switches on the captain's and first officer's ADF control panels to the ANT position, beat frequency oscillator (BFO) switch to OFF, and acquire a local broadcast station in the lower half of the 190-1750 kHz range. Adjust GAIN control to maximum, then adjust volume control (if provided) on audio selector panel for comfortable listening level. Reduce GAIN control setting on ADF control panel if necessary. Check that both controls will vary volume of ADF audio.
　
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