1、 Visual inspection method
The visual inspection method is to perform it immediately after disconnecting the power supply. Without the use of instruments or meters, one can make judgments based on intuitive sensations by utilizing four sensory characteristics: visual, auditory, olfactory, and tactile. This inspection method may have lower accuracy, but it is faster. The intuitive inspection method is particularly useful for checking power faults.
Take a look Observe the machine or component and its external structure. Check whether the button switches, interfaces, and indicator lights are loose, whether the wiring of the circuit board is loose, whether there is virtual soldering, discoloration, cracking, bursting, and other phenomena, and whether the fuse is burnt out, sparking, smoking, deformed, or not stuck. Use your eyes to directly identify and judge.
Er Ting Gently flip the machine or components, sway and listen for any scattered parts or loose screws, and any knocking sounds. Is there any abnormal "squeaking" or "popping" sound when flipping continuously (when powered on). If these phenomena occur, the malfunction may occur in these areas.
Sanwen Smell with your nose for any burning odor, identify the source of the odor, and identify the area where the malfunction may have occurred.
Four touch Touch the transformer casing with your hands (after power failure), do not touch the wiring terminals, as sometimes the voltage can be very high due to the presence of charging capacitors, endangering safety. Feel if it exceeds normal temperature, feels hot, and cannot be touched. Check for overheating or cooling of the power tube. Adjust whether the tube is overheated or not. If these phenomena exist, the problem may arise in these areas.
2、 Probing method
The probing method is to use comparison, segmentation, substitution, simulation and other probing methods to find the fault in the suspected circuit, and then eliminate it. The specific method is as follows:
1. Compare Find a machine of the exact same model as the faulty machine, use the left and right channel components of the same machine in professional equipment to measure the corresponding voltage, resistance, and current quantities, and then compare them to find the fault location.
2. Segmentation Disconnect a certain part of the circuit from other parts, connect an external power supply, inject a signal, and make a judgment.
3. Alternative Replace suspicious components with good ones, or swap left and right channel components, especially for integrated circuit blocks. If the machine returns to normal after replacing the components, it indicates that there is a problem or damage with the component.
4. Simulation Temperature simulation involves heating with a hair dryer or cooling with alcohol to perform temperature performance checks. Vibration simulation involves lightly tapping certain components with a thin plastic insulating rod to observe the working condition of the circuit, which can detect some virtual soldering phenomena and identify the fault location. This method is generally carried out by skilled technicians, otherwise, it is prone to exacerbating the problem.
3、 Static parameter measurement method
The measurement of static parameters must be accompanied by the manufacturer's maintenance manual, which specifies the static working current or voltage at each component endpoint. Use a multimeter to measure the current, voltage, or resistance values of each part of the circuit to see if they match the nominal values.
1. Resistance measurement
Use the ohm range of the multimeter in the X 100 or X 1K range, and do not use the R X 10K range, as this range has a 22.5-volt battery connected to the meter, which is not suitable for measuring transistors and can easily damage them. When measuring in the event of a power outage, if there is a charging capacitor present, it must be fully discharged using an insulated screw cone before proceeding. The resistance in the measurement circuit must be welded at one end, otherwise the measurement will be inaccurate.
2. Voltage measurement
During this measurement process, the influence of the internal resistance of the multimeter on the measured value should be considered. Static measurement values are different from dynamic measurement values (when signals are added), which should be noted. Measure whether the voltage at the pins, resistors, and capacitors of each transistor during static state is consistent with the nominal value, and the relative voltage of the transistor pins can determine whether the transistor is damaged.
3. Current measurement
When using direct measurement, string the ammeter into the circuit and check the current magnitude. When using indirect measurement, the voltage at both ends is measured, and the current value is obtained by subtracting the voltage value from the resistance value. In addition to static parameter measurement, dynamic inspection method can also be used to directly inspect the circuit by injecting signals using a signal source and oscilloscope. This method is direct, accurate, and not easy to damage components. It can also adjust and calibrate circuits and mechanical structures.
