[B737] 客舱广播故障排故指南

客舱广播故障排故指南

系统概述：

When either engine running relay energizes, the gain control relay removes the ground to the PA amplifier. This increases the amplifier gain by 6 db.

If decompression occurs, the oxygen indication relay energizes. At that time, the relay sends a ground to the amplifier and control circuits in the PA amplifier to increase the amplifier gain by an additional 3 db.

The PA audio goes through the REU to the flight crew headsets as sidetone. It also goes to the flight compartment speakers.

The PA amplifier sets the priority of the input signal. These are the PA system audio priorities:

isc][li]Priority 1 - announcement from the flight compartment [/li]

isc][li]Priority 2 - announcement from an attendant [/li]

isc][li]Priority 3 - pre-recorded announcement [/li]

isc][li]Priority 4 - boarding music. [/li]

The lavatories and passenger service units send discrete signals to the PA amplifier to make chime signals.

The function select switch has these positions:

• LOAD (OHMS) 测量负载阻抗正常显示在40欧左右

• TONE 谐音测试

• OPERATE

• LEVEL (VRMS) .输出载波电压，正常在70.7V，可由MASTER GAIN调节

In the LOAD (OHMS) position, the speaker impedance shows on the display. Normally, this impedance is more than 30 ohms. If this impedance is less than 30 ohms, there may be a problem with either a speaker or the interface wiring.

In the TONE position, a continuous tone goes to the speakers. If you do not hear this tone, there may be a problem with either the PA amplifier, the speaker or the interface wiring.

OPERATE is the normal switch position. The display is blank while the switch is in this position.

In the LEVEL (VRMS) position, the output voltage shows on the LED display. the PA amplifier shows the output ac voltage level of the output audio. The LEVEL position disconnects the speakers from the amplifier circuits. It connects a dummy load to internal amplifier circuits.This voltage is normally 70.7 vrms. If you do not see the correct voltage, there may be a problem with either the PA amplifier or the output level adjustment.

Use the master gain adjustment to change the output level. Turn this potentiometer to increase or decrease the gain of the PA amplifier. Normally, you will turn the potentiometer until the display shows 70.7 volts while the function select switch is in the LEVEL position.

故障分析：
一 、客舱及厕所所有喇叭无法播放广播和谐音。

A、现象特征：驾驶舱和客舱的旅客广播均失效，客舱及厕所和前后厨房的喇叭全部无法播放。
B、可能原因：
PA放大器故障
有喇叭出现短路
线路故障
      C、相关手册：
         CMM 23-32-70
      D、故障隔离程序：
         （1）将PA放大器旋钮选择在LOAD位，（正常在40欧姆左右）
              若LOAD显示小于30，继续步骤（4）
         （2）将PA放大器旋钮选择在LEVEL位，（正常为70.7伏）
              若显示不是70.7，调节增益旋钮，若无法调节，更换PA放大器。
         （3）若更换PA无效，检查PA放大器28V DC电源是否正常，检查电源插钉插母是否正常。
         （4）测量喇叭有否短路，脱开客舱所有PSU上的喇叭，测量喇叭输入输出直流电阻在110至180欧，（喇叭共有4个接头分别为：1K、2K、4K、COM，喇叭接1K和COM阻值为110欧 ，喇叭接2K和COM阻值为180欧）若阻值正常，继续步骤（5）
         （5）依据SSM 23-31-11，测量相关线路

图1

图2

二、乘务员无法进行客舱广播

A、现象特征：所有乘务员站位无法进行客舱广播，内话正常，机长广播正常。
B、可能原因：
   驾驶舱客舱广播抑制
   放音机
   REU
C、隔离步骤：
   （1）检查驾驶舱各发话按钮PTT是否有卡滞现象，所有ACP不要选择PA发话，测试乘务员外话是否正常。
        若正常，逐个选择ACP至PA位进行隔离
        若不正常，继续步骤（2）
   （2）脱开放音机电插头，测试乘务员外话是否正常。若正常，更换客舱放音机，若不正常继续步骤（3）
   （3）更换REU   

通过分析SSM，根据故障现象，推测可能原因是放音机内的一个二极管反向导通，导致驾驶舱广播正常，放音机工作正常，而乘务员无法进行广播。

以下是对CMM和SSM的详细分析：

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小发现：乘务员站位喇叭音量，根据SSM 23-31-11我公司738飞机对乘务员站位的喇叭功率选择是不一样的。有以下两种：

因此同一音乐装在不同的飞机上，乘务员站位喇叭音量会有所不同。