Circuit Debugging Methods and Experience Summary
02/13
2020
1. Design circuits based on existing conditions and your acquired knowledge—only in this way can you truly make progress. Avoid simply copying circuit diagrams found online. While it’s perfectly normal to refer to certain parts of other designs, never copy entire circuits wholesale.
2. Select chips based on the overall framework you’ve designed. For power supplies, focus on whether the typical current requirements can be met; for operational amplifiers, pay attention to supply voltage, distortion, slew rate, bandwidth, and other parameters. Choose chips with a margin of safety according to your design—but don’t leave too much headroom, as that would simply be a waste. Conversely, if you need a 10 MHz bandwidth, select an op amp rated for 10 MHz. However, the 10 MHz bandwidth specification for an op amp is only achievable under its own specific lab conditions; in practice, it’s very difficult to attain that level in your actual circuit.
3. When designing schematic diagrams, each chip must be drawn based on the datasheet available on its official website; otherwise, inaccurate information can lead to very serious consequences.
4. Design the PCB layout—here, the primary focus is on ensuring that the chip packages are drawn correctly, especially for surface-mount components. If using through-hole components, the solder vias must be large; otherwise, after you’ve built a multilayer board, the components simply won’t fit, which can be quite frustrating. Routing and layout are a complex art in themselves, so we won’t go into detail here. To briefly touch on it: the signal flow should follow a single, unidirectional path and must not loop back, as such loops can generate significant interference; power traces carrying high currents should be thick and short, and ground planes should never run parallel to power lines.
5. After assembly is complete, be extremely careful when soldering. If the board has multiple power supplies, make sure to fully stabilize the power system before working on other functional chips; otherwise, if you install the functional chips first and the power chip fails to work, it could lead to chip damage. The best approach is to carefully solder each pin one by one—many issues stem from poor soldering. So once you’ve finished soldering, don’t rush—don’t immediately apply power. First, double-check that all pins have been properly soldered. Using the diode test setting on your multimeter is an excellent choice for this step.
6. Weld one level at a time and test it immediately—absolutely do not wait until all the levels are welded before testing. By then, if a problem arises, it’ll be incredibly difficult to pinpoint where it occurred.
7. If you follow the above steps, everything should be fine except for the high‑frequency signals.
What should we do if something goes wrong?
First, check the schematic diagram to ensure it’s correct—any mistakes here will render your debugging efforts futile.
Second, if the schematic is没问题, then check whether the power supply is functioning properly (note: do not apply power—this test is to verify whether the connections are properly established).
Third, if there are no issues with the power connection, then check whether there are any problems with the other circuit connections.
Fourth, if there are no issues with the circuit connections, you have two options: either turn on the power and check whether the current is normal—perhaps the voltage regulator is limiting the current—or first desolder the chip and then recheck whether the power supply is functioning properly (especially if there’s a voltage regulator chip involved).
Fifth, to summarize: when a circuit malfunctions, it usually comes down to just a few common issues: 1. Incorrect design principles; 2. Power supply errors; 3. Wiring errors; 4. Severe interference—especially at high frequencies. As for PCB layout problems, it’s best to re‑route the board.
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