HF Communication System schematic  5C8 
23-11-02  Figure 2 (Sheet 1)  Jun 20/88 
Page 12 
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5E6  HF Communications System Schematic 
Feb 20/87  Figure 3 (Sheet 2)  23-11-02 
Page 13 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

HF COMMUNICATION SYSTEM - TROUBLE SHOOTING
EFFECTIVITY
Airplanes with Collins 628T-2A Transceiver
1. General
A.  Trouble spots in the HF communication system can be most easily corrected by replacing a suspected malfunctioning component. If the system is not operative after assumed malfunctioning components have been replaced by known operative components, check airplane wiring.
B.  To decrease the number of unscheduled removals, confirm that the condition stated in the flight report exists prior to replacing system components. If HF system is reported to be inoperative on one or two specific frequencies, a precautionary check of the equipment should be made to confirm the report and that the problem is repetitive. The trouble may be due to the area and position of the airplane in respect to the ground station, or to other conditions existing at the time. Also ensure the flight interphone system is operating properly so that poor communication attributed to the HF system is not actually due to a faulty isolation amplifier in an audio selector panel.
C.  Before attempting to operate HF system, ensure all HF circuit breakers on load control centers P18 and P6 are closed and power is available to them. Since no terminals are available for power measurements, voltages are most easily checked by using the meter on the front of the transceiver. Allow the system to warm up for 15 minutes before trouble shooting.
5E2
Feb 20/88 23-11-02 Page 101
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
2. Trouble Shooting Chart HF COMMUNICATIONS SYSTEM - ADJUSTMENT/TEST

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23-11-02 Page 102  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Jun 20/84 

EFFECTIVITY
Airplanes with Collins 628T-2A Transceivers
1.  General
A.  The following test should be used to check the operation of an HF system after a system component has been replaced or repaired. Conduct test using only authorized test frequencies and check to ensure frequency is not in use before transmitting.
B.  The airplane should not be in or near a large metallic structure, such as a hangar or tower, which may attenuate RF energy.
2.  HF Communication System Test
A.  Prepare to Test
(1)  
Provide ground power to the airplane and energize buses on load control center P18 and P6.

(2)  
Ensure all HF circuit breakers and interphone audio selector panel circuit breakers are closed.

(3)  
Turn on HF systems and allow 15 minutes for warmup.

(4)  
Check flight interphone system and ensure audio selector panels are operable (Ref 23-52-0).

B.  Test HF Communication System
(1)  
At captain's and first officer's stations, select HF-1 on audio selector panel and activate the HF audio monitor.

(2)  
Turn HF-1 control panel mode selector switch to AM and tune system to several WWV frequencies.

NOTE:  WWV transmits on 5, 10, and 15 MHz. The RF signals are modulated by pulses at 1 Hz and also by standard audio frequencies alternating between 440 and 600 Hz. WWV transmissions are continuous except for a 4-minute interruption beginning approximately 45 minutes after the hour.
5E2
Feb 20/88 23-11-02 Page 501
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(3)  
Perform an approximate frequency check on the transceiver by listening to WWV with the mode selector switch in the USB and AM positions. Reception shall be satisfactory in all positions at both captain's and first officer's stations.

(4)  
Tune HF-1 system to an authorized test frequency and press a microphone push-to-talk button. A 1 kHz tone shall be heard during system tuning. WWV reception shall return when HF-1 system keying is released.

(5)  
Adjust RF SENS (RF gain) control on HF-1 control panel to maximum. If subsequent tests reveal RF overloading is occurring, back off control to point where overload condition just disappears.

(6)  
Tune HF-1 system to several active channels and establish communication. Reception should be approximately equal on all channels. Check operation with mode selector switch in AM and USB positions. Communication shall be satisfactory in al1 positions.
　
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