The general diagnosis sequence for complex SMT equipment electrical faults is: symptom analysis - equipment inspection - determination of the faulty part - line inspection - replacement or repair - post-repair performance inspection.

 

1. Symptom analysis. Symptom analysis is the process of collecting and judging all possible information about the original status of the fault. All information should be carefully analyzed before the fault signs are disturbed.

 

2. Equipment inspection. Based on the preliminary conclusions and doubts derived from the symptom analysis, a more detailed examination of the equipment is carried out, especially in those areas considered most likely to be faulty. It should be noted that unnecessary disassembly of the equipment should be avoided at this stage to prevent further failures.

 

3. Determination of the fault location. Maintenance personnel must fully understand the control principles and structure of the system. If there is a lack of system diagnostic data, maintenance personnel need to correctly divide the entire equipment or control system into several functional blocks, and then check whether the input and output of these functional blocks are normal.

 

4. Line inspection, replacement and repair. These two steps are closely related. Line inspection can be carried out in a similar way to determining the fault location. First, find out the faulty components or components that need to be replaced, and then carry out effective repairs.

 

5. Performance inspection after repair. After the repair is completed, the maintenance personnel should conduct further inspections to confirm that the fault has indeed been eliminated and the equipment can run well.

 

When the electrical system of the equipment fails, do not rush to disassemble it. First, you must understand the cause, process, scope, and phenomenon of the failure of the electrical equipment. Be familiar with the basic working principles of the equipment and electrical system, analyze each specific circuit, and clarify the principle. Carefully analyze the interconnections between circuits at all levels and the ins and outs of signals in the circuit. Based on practical experience and careful thinking, I have summarized the "Eight Sequences" formula for quick and effective maintenance techniques.

 

1. "Ask first and then take action, and become familiar with the principles and structure." - For faulty electrical equipment, do not rush to take action. You should first ask about the process and phenomenon of the fault. For unfamiliar equipment, you should first familiarize yourself with the circuit principles and structural features and abide by the corresponding rules. Before disassembly, you must be fully familiar with the function, location, connection method and relationship with other surrounding devices of each electrical component. If there is no assembly diagram, you should draw a sketch and mark it while disassembling.

 

2. "Go outside first and then inside, and exclude dismantling and repairing the outside." - You should first check the equipment for obvious cracks and defects, understand its maintenance history, service life, etc., and then inspect the inside of the machine. Before disassembly, the surrounding fault factors should be sorted out and dismantled only after it is determined to be an internal fault. Otherwise, blind disassembly may make the equipment worse as it is repaired.

 

3. "Check the mechanical first, then the electrical, and use instruments to record carefully" - only conduct electrical inspections after confirming that the mechanical parts are fault-free. When checking for circuit faults, you should use testing instruments to find the fault location. After confirming that there is no bad contact fault, you can then check the operating relationship between the circuit and the machine in a targeted manner to avoid misjudgment.

 

4. "Look at the static state first and then the movement, and check carefully before turning on the power" - First, inspect the electrical equipment without powering on. Then perform maintenance on the electrical equipment while the power is on. When repairing many failed electrical equipment, power cannot be turned on immediately, otherwise the scope of the fault will be artificially expanded, more components will be burned, and undue losses will occur. Therefore, before powering on the faulty machine, conduct a resistance measurement and take necessary measures before powering on for maintenance.

 

For example, when the equipment is not powered on, determine the quality of the buttons, contactors, thermal relays and fuses of the electrical equipment to determine the location of the fault. Power on the test, listen to the sound, measure parameters, determine the fault, and finally perform repairs. For example, when the motor is missing a phase, if the three-phase voltage value cannot be determined, you should listen to the sound and measure the voltage of each phase individually to determine which phase is missing.

 

5. "Clean the dirt first and then repair, otherwise the electricity will be blocked due to dirt and dust" - For electrical equipment with heavy pollution, clean the buttons, wiring points, and contact points first, and check whether the external control keys are malfunctioning. Many faults are caused by dirt and conductive dust particles, and the faults are often eliminated once cleaned.

 

6. "Check the power supply first and then the equipment, and you will get twice the result with twice the result if there are frequent faults." - The failure rate of the power supply part accounts for a high proportion of the entire faulty equipment, so checking the power supply first can often get twice the result with half the effort and quickly find the fault point.

 

7. "Check the public first and then the private, and the energy information is not sent" - If the public circuit of any electrical system fails, its energy and information cannot be transmitted and distributed to each specific dedicated circuit, and the functions and performance of the dedicated circuit will not work. . If the power supply of an electrical equipment fails, the entire system cannot operate normally, and the energy and information transmitted to various special circuits cannot be realized. Therefore, by following the order of public circuits first, then dedicated circuits, faults in electrical equipment can be quickly and accurately eliminated.

 

8. "Fix common problems first and then difficult ones, and accumulate experience to improve your skills" - Electrical equipment is often prone to the same type of faults, which is a "common problem". Because common diseases are relatively common and accumulated experience is rich, they can be eliminated quickly. In this way, you can concentrate your energy and time on eliminating rare, difficult, and weird incurable diseases, simplify the steps, narrow the scope, and increase the speed of maintenance.

 

Sum up experience and improve efficiency. There are many types of electrical equipment failures. After any faulty electrical equipment has been overhauled, the fault phenomenon, cause, maintenance process, skills, and experiences should be recorded in a special notebook to learn and master the electromechanical theoretical knowledge of various new electrical equipment, become familiar with its working principles, and accumulate maintenance experience. Turn your experience into theory. Only under the guidance of theory and detailed analysis of specific faults can faults be eliminated accurately and quickly. Only in this way can you train yourself to be an expert in troubleshooting electrical faults.