Circuit board maintenance and inspection methods are primarily categorized into the following ten types:
1. Offline Measurement
When the circuit board is not soldered into the circuit, compare the DC resistance values between the pins with the known normal DC resistance values of a circuit board of the same model to determine whether it is functioning correctly.
2. Online Measurement
Measure the voltage, resistance, and current values at each pin of the circuit board while it is in operation to assess if the circuit board is functioning properly or if it has any damage.
3. Substitution Method
Replace the circuit board under test with a known-good circuit board of the same model and specifications. This helps to determine if the circuit board has any issues and facilitates repairs if needed.
4. Separation Test
1. A fault-checking method that isolates the circuit sections related to the fault in electronic equipment to pinpoint the fault’s location. This method involves performing multiple inspections to confirm and exclude parts of the circuit, gradually narrowing down the potential fault area until it is located and the circuit board is repaired.
2. Signal Injection
Use different output signals from an external signal source as known test signals and observe the results on the terminal indicator of the tested electronic device. Select the appropriate signal source to obtain known signals for various indicators; check from the later stages to the earlier ones by injecting known signals into the input terminal of the indicator, moving sequentially from the subsequent to the preceding stages. In industrial circuit board maintenance, inject known and varied test signals into each circuit stage’s input terminals, and monitor the terminal surface indicator’s reaction to determine the fault’s location and analyze the cause.
3. Intuitive Check
This method involves checking the PCB circuit board using human intuition—sight, smell, hearing, and touch—without any equipment or soldering. Intuitive inspection is the most basic method for detecting equipment failures.
4. Signal Tracking Method
Utilize a single test signal and tools like an oscilloscope or electronic voltmeter to perform step-by-step checks from front to back. This method allows for in-depth quantitative inspection of all circuit stages and quickly identifies the fault location.
5. AC Short Circuit Method
Bypassing a section of the electronic equipment circuit under test with capacitors of appropriate capacity and voltage is the method used. This approach is effective for identifying circuit sections that cause power interference and parasitic oscillations in the electronic equipment.
6. Parametric Test
This method involves using instruments to measure voltage, current, component values, and device parameters within the electronic circuit. Resistance is typically measured with the power off, while voltage and current are measured with the power on, or components are removed for parameter measurements.
7. Waveform Observation Method
Use an oscilloscope to observe waveforms from faulty and related parts of the electronic equipment. Analyze differences in waveform shape, amplitude, and time parameters compared to normal waveforms to diagnose the fault and determine repair measures.
8. PCB Circuit Board Storage Method
After final inspection, PCBs awaiting shipment or assembly should be stored properly to prevent performance degradation. Avoid prolonged storage times that may affect product performance.
9. Vacuum Packaging Storage
To prevent direct contact with water and long-term exposure to humid air, vacuum-pack the PCB board. Surround the packaging with bubble wrap and include moisture-proof beads. Label and classify, then store in a dry, ventilated place away from direct sunlight.
10. Brush with Three Anti-Paints
PCBs with surface treatments like immersion gold, electro-gold, spray tin, or silver plating can typically be stored for 6 months, while those with immersion silver, tin, or OSP can be stored for about 3 months. Applying a layer of conformal paint to unused PCBs can extend their storage life to approximately 9 months.
11. Temperature and Humidity Control
Maintain the storage warehouse temperature at 23±3°C with 55±10% RH. Ideal conditions are less than 25°C and less than 65% relative humidity, with no corrosive gases present in the environment.
