1. How to repair circuit boards without schematics?
1. To “have a clear picture”
It’s essential to deeply grasp the principles of typical circuits and become familiar with them. Schematics may be static, but the thoughts in your mind are dynamic, allowing for analogy, reasoning, and deduction. For instance, a switching power supply is always linked to the oscillating circuit, switching transistor, and transformer. During inspection, check for circuit oscillation, capacitor integrity, and the condition of transistors and diodes. Regardless of the specific switching power supply, their operation is quite similar, eliminating the need for a detailed schematic.
2. Focus on the order of maintenance
Be mindful of the maintenance sequence to find the most efficient path to resolve issues, avoiding haphazard disassembly that could exacerbate the problem. Maintenance is akin to a doctor’s treatment, so it’s important to “observe, listen, and inquire.”
3. Excel at summarizing patterns
Typically, after accumulating a certain level of repair experience, it’s crucial to analyze and summarize the causes behind each component’s failure. Was it due to improper operation, insufficient maintenance, poor design, substandard component quality, or natural aging? By conducting these analyses, you will gain insights that will assist you in addressing similar failures in the future, even on different circuit boards.
4. **Become Proficient in Information Retrieval**
Since the advent of the Internet, locating information has become remarkably straightforward. Almost all equipment principles and circuit theories you may not understand can be found online, along with any IC details you need.
5. **Essential PCB Testing Equipment is Required**
If you consider maintenance your business, investing in certain tools is essential. The brands of electric soldering irons, multimeters, and standard disassembly tools should be reliable. If possible, acquire a 100M dual-trace oscilloscope and, ideally, an online maintenance tester.
6. **Fault Characteristics and Repair of Industrial PCB Capacitor Failures**
Capacitor damage accounts for the most frequent failures in electronic equipment, with electrolytic capacitors being the most commonly affected.
The symptoms of capacitor failure include: 1. Reduced capacitance; 2. Total loss of capacitance; 3. Leakage; 4. Short circuit.
Capacitors serve various functions in circuits, and the faults they cause exhibit distinct characteristics. In industrial control boards, digital circuits dominate, with capacitors mainly used for power supply filtering, while fewer capacitors are utilized for signal coupling and oscillation. If an electrolytic capacitor in a switching power supply fails, the power supply may stop oscillating, resulting in no voltage output, or the output voltage may become poorly filtered, causing logical chaos due to voltage instability. In any device, if a capacitor is connected between the positive and negative terminals of a digital circuit’s power supply, the resulting fault will be similar.
7. **Characteristics and Diagnosis of Resistor Damage**
Resistors are the most abundant components in electrical equipment, yet they do not have the highest failure rate. Open circuits are the most prevalent type of resistor failure. Resistance increases are uncommon, and decreases are rare. Common types include carbon film resistors, metal film resistors, wire-wound resistors, and fuse resistors. The first two are the most widely utilized. Notably, low resistance (below 100Ω) and high resistance (above 100kΩ) tend to have higher failure rates, while mid-range resistances (hundreds of ohms to tens of kilo-ohms) are less likely to fail. Low-resistance failures often result in burning and blackening, making them easy to identify, while high-resistance failures are less common. Wire-wound resistors, generally used for high current limiting, can show signs of burning such as blackening or surface cracking, although some may exhibit no visible damage. Cement resistors, a type of wire-wound resistor, may break without leaving any visible traces when burned out. When fuse resistors fail, a small piece of the surface may explode, but they typically show no signs of burning or blackening. Based on these characteristics, focusing on resistance checks can help quickly identify damaged resistors.
8. **Determining the Functionality of Operational Amplifiers**
An ideal operational amplifier exhibits “virtual short” and “virtual break” characteristics, which are crucial for analyzing linear applications in op-amp circuits. To maintain linear applications, the op-amp must operate in a closed loop (negative feedback). In the absence of negative feedback, the op-amp functions as a comparator. To assess device quality, first determine whether it is used as an amplifier or as a comparator within the circuit.
9. **A Simple Trick for Testing SMT Components with a Multimeter**
Testing and repairing small SMD components can be challenging with standard multimeter leads. This can lead to short circuits or make it difficult to make contact with the metal parts of component pins, especially on circuit boards with insulating coatings. Here’s a straightforward method that can greatly simplify the testing process.
10. **Repairing Circuit Board Power Supply Short-Circuit Faults**
When dealing with a short circuit in the public power supply of a circuit board, the fault can often be severe, as many devices share the same power source, making each one a potential suspect. If the board has few components, using a “ground hoe” technique may help locate the short-circuit point. However, if the board is densely populated, success with this method can be hit-or-miss. A more effective approach is recommended here, which can lead to quicker identification of the fault.
11. **A Simple Eraser Can Solve Big Problems**
As industrial control boards increasingly utilize golden fingers to connect to slots, environmental factors like dust, humidity, and corrosive gases can lead to contact issues. While replacing the board might seem like a solution, it can be costly, particularly for imported equipment. A simple yet effective solution is to use an eraser to clean the golden fingers and then re-test the machine; this may resolve the issue.
12. **Analyzing Electrical Faults in Varying Conditions**
Various electrical faults may arise in good times and bad, including:
1. Poor contact—issues between the board and slot, broken cables, or improperly soldered components;
2. Signal interference—faults may only manifest under specific conditions due to excessive interference affecting the control system;
3. Poor thermal stability of components—electrolytic capacitors are often the most sensitive, followed by other capacitors, transistors, diodes, ICs, and resistors;
4. Moisture and dust on the circuit board—these can create conductive paths, affecting resistance and potentially leading to malfunctions;
5. Software considerations—parameters adjusted via software can be set too low, leading to alarms when operating conditions meet certain critical thresholds.
13. **How to Quickly Locate Component Information**
Modern electronic products are increasingly diverse, leading to a wide array of components. In circuit maintenance, particularly for industrial PCBs, many components may be unfamiliar or unheard of. Even when comprehensive information is available for a specific board, the lack of an efficient search method can significantly hinder maintenance efficiency. In industrial electronic repair, time is money, and efficiency is paramount.
1. To “have a clear picture”
It’s essential to deeply grasp the principles of typical circuits and become familiar with them. Schematics may be static, but the thoughts in your mind are dynamic, allowing for analogy, reasoning, and deduction. For instance, a switching power supply is always linked to the oscillating circuit, switching transistor, and transformer. During inspection, check for circuit oscillation, capacitor integrity, and the condition of transistors and diodes. Regardless of the specific switching power supply, their operation is quite similar, eliminating the need for a detailed schematic.
2. Focus on the order of maintenance
Be mindful of the maintenance sequence to find the most efficient path to resolve issues, avoiding haphazard disassembly that could exacerbate the problem. Maintenance is akin to a doctor’s treatment, so it’s important to “observe, listen, and inquire.”
3. Excel at summarizing patterns
Typically, after accumulating a certain level of repair experience, it’s crucial to analyze and summarize the causes behind each component’s failure. Was it due to improper operation, insufficient maintenance, poor design, substandard component quality, or natural aging? By conducting these analyses, you will gain insights that will assist you in addressing similar failures in the future, even on different circuit boards.
4. **Become Proficient in Information Retrieval**
Since the advent of the Internet, locating information has become remarkably straightforward. Almost all equipment principles and circuit theories you may not understand can be found online, along with any IC details you need.
5. **Essential PCB Testing Equipment is Required**
If you consider maintenance your business, investing in certain tools is essential. The brands of electric soldering irons, multimeters, and standard disassembly tools should be reliable. If possible, acquire a 100M dual-trace oscilloscope and, ideally, an online maintenance tester.
6. **Fault Characteristics and Repair of Industrial PCB Capacitor Failures**
Capacitor damage accounts for the most frequent failures in electronic equipment, with electrolytic capacitors being the most commonly affected.
The symptoms of capacitor failure include: 1. Reduced capacitance; 2. Total loss of capacitance; 3. Leakage; 4. Short circuit.
Capacitors serve various functions in circuits, and the faults they cause exhibit distinct characteristics. In industrial control boards, digital circuits dominate, with capacitors mainly used for power supply filtering, while fewer capacitors are utilized for signal coupling and oscillation. If an electrolytic capacitor in a switching power supply fails, the power supply may stop oscillating, resulting in no voltage output, or the output voltage may become poorly filtered, causing logical chaos due to voltage instability. In any device, if a capacitor is connected between the positive and negative terminals of a digital circuit’s power supply, the resulting fault will be similar.
7. **Characteristics and Diagnosis of Resistor Damage**
Resistors are the most abundant components in electrical equipment, yet they do not have the highest failure rate. Open circuits are the most prevalent type of resistor failure. Resistance increases are uncommon, and decreases are rare. Common types include carbon film resistors, metal film resistors, wire-wound resistors, and fuse resistors. The first two are the most widely utilized. Notably, low resistance (below 100Ω) and high resistance (above 100kΩ) tend to have higher failure rates, while mid-range resistances (hundreds of ohms to tens of kilo-ohms) are less likely to fail. Low-resistance failures often result in burning and blackening, making them easy to identify, while high-resistance failures are less common. Wire-wound resistors, generally used for high current limiting, can show signs of burning such as blackening or surface cracking, although some may exhibit no visible damage. Cement resistors, a type of wire-wound resistor, may break without leaving any visible traces when burned out. When fuse resistors fail, a small piece of the surface may explode, but they typically show no signs of burning or blackening. Based on these characteristics, focusing on resistance checks can help quickly identify damaged resistors.
8. **Determining the Functionality of Operational Amplifiers**
An ideal operational amplifier exhibits “virtual short” and “virtual break” characteristics, which are crucial for analyzing linear applications in op-amp circuits. To maintain linear applications, the op-amp must operate in a closed loop (negative feedback). In the absence of negative feedback, the op-amp functions as a comparator. To assess device quality, first determine whether it is used as an amplifier or as a comparator within the circuit.
9. **A Simple Trick for Testing SMT Components with a Multimeter**
Testing and repairing small SMD components can be challenging with standard multimeter leads. This can lead to short circuits or make it difficult to make contact with the metal parts of component pins, especially on circuit boards with insulating coatings. Here’s a straightforward method that can greatly simplify the testing process.
10. **Repairing Circuit Board Power Supply Short-Circuit Faults**
When dealing with a short circuit in the public power supply of a circuit board, the fault can often be severe, as many devices share the same power source, making each one a potential suspect. If the board has few components, using a “ground hoe” technique may help locate the short-circuit point. However, if the board is densely populated, success with this method can be hit-or-miss. A more effective approach is recommended here, which can lead to quicker identification of the fault.
11. **A Simple Eraser Can Solve Big Problems**
As industrial control boards increasingly utilize golden fingers to connect to slots, environmental factors like dust, humidity, and corrosive gases can lead to contact issues. While replacing the board might seem like a solution, it can be costly, particularly for imported equipment. A simple yet effective solution is to use an eraser to clean the golden fingers and then re-test the machine; this may resolve the issue.
12. **Analyzing Electrical Faults in Varying Conditions**
Various electrical faults may arise in good times and bad, including:
1. Poor contact—issues between the board and slot, broken cables, or improperly soldered components;
2. Signal interference—faults may only manifest under specific conditions due to excessive interference affecting the control system;
3. Poor thermal stability of components—electrolytic capacitors are often the most sensitive, followed by other capacitors, transistors, diodes, ICs, and resistors;
4. Moisture and dust on the circuit board—these can create conductive paths, affecting resistance and potentially leading to malfunctions;
5. Software considerations—parameters adjusted via software can be set too low, leading to alarms when operating conditions meet certain critical thresholds.
13. **How to Quickly Locate Component Information**
Modern electronic products are increasingly diverse, leading to a wide array of components. In circuit maintenance, particularly for industrial PCBs, many components may be unfamiliar or unheard of. Even when comprehensive information is available for a specific board, the lack of an efficient search method can significantly hinder maintenance efficiency. In industrial electronic repair, time is money, and efficiency is paramount.
