How to debug the public address system

The debugging of the broadcasting system mainly refers to the comprehensive and routine inspection of the equipment installation process after the installation and construction of the broadcasting system is completed, as well as the opening test and sound quality evaluation. The main work contents are: transmission line inspection, connection inspection, insulation resistance Measurement, grounding resistance measurement, antenna debugging, power supply test, system turn-on test, sound pressure measurement and sound quality evaluation, etc .:

1. Transmission line inspection

The broadcast transmission line is divided into indoor and outdoor wiring. During the inspection, the terminal of the tested line should be disconnected from the device. According to the construction drawing and broadcast system diagram, check whether the transmission wiring is correct and whether there is a short circuit. Open circuit, mixed line and other faults; whether the terminal number is complete and correct, and whether the terminal is welded. Eliminate the discovered faults one by one, and re-tighten the connection terminals; whether the connection of each plug and socket is welded, whether the wiring is correct and reliable, and whether the shield connection is complete and good, which meets the requirements.

2. Matching inspection

According to the construction drawings, check whether the connection between the transformers on each circuit or speaker equipment is correct. In particular, the connection terminals of multi-tap transformers are often prone to be misconnected. Pay attention to check for missing and multiple connections. ; Check if the transformer model, capacity and impedance match according to the picture,

3. Determination of insulation resistance

Disconnect the two terminals of the broadcast line, and use a 500V megohmmeter to measure the insulation resistance between the lines. The measurement items are: wire-to-wire and wire-to-earth insulation resistance. The insulation resistance is generally not less than 0.5MΩ. The resistance of each circuit should be measured in sub-circuits. The measurement value should be filled in the record and handed over to the construction unit as the content of the debugging report .

4. Ground resistance measurement

The grounding resistance of the broadcasting system is mainly carried out on the grounding electrode of the broadcasting room; a grounding resistance tester is used for the measurement.

The power-frequency grounding resistance of broadcasting room amplifiers, lightning arresters, etc. is generally not greater than 10Ω. When the capacity of the broadcasting system is more than 150 W, if it is difficult to set the grounding electrode alone, a group of grounding electrodes can be used in conjunction with electrical equipment Grounding requirements The grounding resistance should not be greater than 4Ω, and a dedicated grounding trunk should be provided.

V. Power supply test

Measure the AC power supply voltage, the power supply circuit should not be short-circuited or open-circuited, do the on-off operation test on the power switch, check the power supply display signal; the backup power supply interchange device check test, the battery output voltage measurement; charge the rectifier Check and measure the device; do a simulated power outage test to verify whether the mutual power supply device can work reliably.

6. System opening test

The problems found in the above inspections have all been revised. After all inspection tests meet the requirements, the system opening test can be carried out. The system opening test should be opened by equipment and one by one.

1. Turn on the amplifier

First disconnect all output lines, pull out all input signal plugs, turn the amplifier's "volume" adjustment knob to the minimum, turn on the power, turn on the amplifier switch, and observe whether the displayed signals are normal and whether there is machine noise.

2. The pre-amplifier is turned on

When everything is normal after the amplifier is turned on, the pre-amplifier can be turned on. Turn on the power of the pre-amplifier, observe the various displays, and connect the connection line between the pre-amplifier and the power amplifier.

3. Microphone test

When the amplifier and preamplifier work normally, set the "volume" knobs of the preamplifier and amplifier to the minimum, insert the microphone plug, give the microphone a sound signal, adjust the "volume" knob, and listen to the sound output on the jian listening headphones. At this time, the "function" knob of the amplifier or preamplifier is turned to the microphone position. When one microphone jack is tested, use the same method to test each microphone input channel.

4. Recorder input

Turn the pre-amplifier or amplifier "function" knob to the input file of the recorder, and connect the input circuit of the recorder, play the recording tape, adjust the "volume" size, and observe the input signal, distortion and noise.

5. Opening test of receiving tuner

Turn on the power of the tuner, receive the broadcast program, test the receiving situation, and adjust the direction of the FM receiving antenna repeatedly according to the receiving effect of the FM broadcast to obtain the best listening effect. And observe the interference and distortion.

6. Output circuit test

Input the pre-amplifier or amplifier into the recording or record signal, turn the "Volume" to the minimum, turn on the loudspeaker equipment, adjust the "Volume" to the middle position, observe the volume, clarity and noise of the standby speaker; "Volume" is turned to the maximum, observe whether there is distortion; and adjust the speaker volume controller to listen to the sound distortion and volume changes. For severely distorted speakers, the transformer between the wires and the speaker coil should be inspected, and if problems are found, they should be repaired or replaced.

Use the above method to test each speaker device circuit. If the speakers on each circuit are pronounced normally (ie, low noise, clear, and low distortion), you can turn on all speakers and sound columns, adjust the volume, and repeat the test many times. To eliminate various hidden dangers in installation and construction.