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Fault Inspection Method of Public Address System


After the initial debugging or operation of the broadcasting system fails, we usually find the faulty equipment according to the program signal process and carry out simple maintenance. If the equipment failure is more complex, or the manufacturer warranty and does not allow the user to repair, it should be directly returned to the manufacturer for repair. The following is a simple method of maintenance.

1. Visual inspection method

Visual inspection method is immediately after the power is disconnected. Do not use instruments, meters, with intuitive feeling, to mobilize the visual, auditory, olfactory, tactile and other senses, to judge. Although this inspection method is less accurate, it is fast, and the visual inspection method is especially useful for power failure inspection.

Look: Observe the machine or component and its external structure. Check whether the key switch, interface and indicator light are loose, whether the connecting thread of the circuit board falls off, whether there is virtual welding, discoloration, crack, burst and other phenomena, whether the fuse is blown, lit, smoke, deformed, not stuck and other problems, and use eyes to directly identify and judge.

Second listening: gently turn the machine or parts, swing, listen to whether there are parts scattered or screws falling off, whether there is a collision sound. Do continuous turnover to see if there is any abnormal "squeaking" sound or "popping" sound (when power is on). If there are these phenomena, the fault may appear in these places.

Three sniffing: use your nose to smell if there is a burning smell, find the source of the smell, the fault may be a place that emits peculiar smell.

Four touch: touch the transformer shell by hand (after power failure), do not touch the terminal, because sometimes due to the existence of charging capacitor, the voltage is very high, endangering safety. Feel whether it exceeds the normal temperature, is hot and cannot be touched. Whether the power tube is overheated or cold. Adjust whether the tube is overheated or cold. If there are these phenomena, the problem may appear in these places.

2. Tentative method

The test method is to use comparison, segmentation, substitution, simulation and other test methods for the suspected part of the circuit to find the fault and then eliminate it. Specific methods are as follows:

Comparison: Find a machine of exactly the same type as the fault machine, measure the voltage, resistance and current of the corresponding part, and then compare them to find the fault.

Segmentation: disconnect a certain part of the circuit from other parts, connect the external power supply, inject signals, and make judgments.

Substitution: Replace suspected components with good components, or swap left and right channel components, especially for integrated circuit blocks. If the machine returns to normal after a part swap, the part is defective or damaged.

Simulation: temperature simulation, the use of hair dryer heating, or alcohol cooling, temperature performance inspection, vibration simulation is the use of fine plastic insulation rod tap some parts, look at the circuit working conditions, you can find some virtual welding phenomenon, check the fault. This method is generally carried out by skilled technicians, otherwise, it is easy to aggravate the phenomenon of failure.

3. Static parameter measurement method

The measurement of static parameters shall hold the maintenance manual of the manufacturer's equipment, indicate the static working current or voltage of each component endpoint, and use a multimeter to measure the current, voltage or resistance value of each part of the circuit to see if it is consistent with the nominal value.

Resistance measurement: use the ohm gear × 100 or × 1K gear of the multimeter, and do not use the R× 10K gear, because the 22.5 volt battery is connected to the meter in this gear, which is inappropriate for transistor measurement and easy to damage the transistor. In the case of power failure, if there is a charging capacitor, it must be fully discharged with an insulated screw taper. One end of the resistance in the measurement circuit must be welded, otherwise the measurement is not accurate.

Voltage measurement: In the process of making this measurement, the influence of the internal resistance of the multimeter on the measured value should be considered. It should be noted that static measurements are not the same as dynamic measurements (when the signal is added). Measure whether the terminal voltage of each transistor pin, resistor and capacitor is consistent with the nominal value when static, and whether the tube is damaged can be judged by the relative voltage of the transistor pin.

Current measurement: when using direct measurement, string the ammeter into the circuit and check the current. When indirect measurement is used, the voltage at both ends is measured, and the voltage value is removed by the resistance value to obtain the current value.

In addition to static parameter measurement, but also the use of dynamic inspection method, the use of signal source and oscilloscope, direct inspection of the injection signal, the circuit to judge. This method is direct, accurate, and not easy to damage components, but also on the circuit and mechanical structure adjustment and proofreading.

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