(2)  
Do not use a megohmmeter at these locations:

(a)  
Area adjacent to or below a wing fuel tank vent, five foot (1.524 meters) diameter column, from vent to ground.

(b)  
Zero to 18 inches (457 mm) above the ground in the area around the airplane.

(c)  
Make sure that:
1) Area is well ventilated.
2) Metal workstands are grounded.
3) Megohmmeter is plugged into a grounded receptacle.
4) Megohmmeter is insulated from metal work stands.

H.  Measure, for all dischargers, the resistance between the end of discharger tip and the discharge base using a megohmmeter of at least 500 volts. To make a good surface contact with the end of the discharger tip, wet a paper towel, cotton cloth or sponge with tap water and place in contact with entire surface of end of discharger tip. Place megohmmeter leads on base and on wet material at end of tip. If reading is high, verify that the wet material is adhering to the meter lead and to the end of the discharger tip. Add more water if necessary and measure again. Take lowest reading.
(1)  Discharger resistance shall be within the limits of 6-100 megohms for trailing edge and tip types of dischargers.
NOTE: Dischargers failing to meet the resistance check should be replaced.
I.  Dischargers exhibiting any damage or failure to meet the resistance check requirements should be replaced.
J.  Put the airplane back to its usual condition.
(1)  Put the hydraulic systems for the flight control surfaces back to the usual condition (Ref 27-11-0 MP, 27-21-0 MP, 27-31-0 MP).
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VOICE RECORDER SYSTEM - DESCRIPTION AND OPERATION
1. General (Fig. 1)
A.  The voice recorder system records and preserves a continuing record of the latest 30 minutes of flight crew communications and conversation. The voice recorder system has four separate inputs for simultaneous recording of any communications in the flight compartment on 4-track tape. Channel one receives audio from the first observer's audio selector panel, channel two receives audio from the first officer's audio selector panel and channel three receives audio from the captain's audio selector panel. Channel four audio is taken from a microphone pickup in the voice recorder control panel.
B.  The voice recorder system (Fig. 1) consists of a voice recorder unit installed on the right side of the airplane in the aft cargo compartment; a voice recorder control panel installed in the pilots' overhead panel P5; interconnecting wiring; and relay contacts in landing gear accessory unit module M338.
C.  An erase head in the recorder unit automatically erases previously recorded information prior to recording. A 30-minute length of closed loop magnetic tape then provides a record of the previous 30 minutes of conversation. An internal monitoring circuit ensures proper operation of the recording mechanism and circuits. Audible and visible indications derived from the monitoring circuits are presented at a meter and a jack when the test switch on the control panel is operated. The entire tape may be erased after the airplane has landed and the parking brake has been set.
D.  An underwater locating device (ULD) is attached to the voice recorder front panel, although not a part of the voice recorder system. The ULD is a beacon that automatically energizes when the unit is immersed in water, thereby assisting to locate the recorder in case of an accident in the ocean or other body of water.
E.  Operating power for the voice recorder system is 115 volts, 400 Hz ac obtained from the ac bus No. 1 through the VOICE RECORDER circuit breaker on P6.
503 
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H45004
Voice Recorder System Component Location  580 
23-71-0  Figure 1  Oct 20/84 
Page 2 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

2.  Voice Recorder Control Panel
A.  The voice recorder control panel is located in the pilots' overhead panel P5. It contains a microphone and preamplifier, a meter, a test pushbutton, a headphone jack, and an erase pushbutton. The microphone and its preamplifier pick up the conversation in the flight compartment and supply audio to channel 4 of the voice recorder unit. When the TEST pushbutton is pressed, it activates a test circuit in the recorder unit. If all channels are recording properly, the meter needle indicates in the green area and a 600-Hz test tone is supplied to the HEADSET jack. The ERASE pushbutton will erase the entire tape in the recorder if held for a minimum of two seconds. However, the bulk erase circuit will operate only with the airplane on the ground, power applied to the airplane, and the parking brake set.
　
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