How to Test a Circuit Board?
- Issue Time
It is inevitable that the circuit board will fail. As long as we master the way to test the circuit board, we can know the problem. The following is the process of testing the circuit board.
Before testing the circuit, you need to be well prepared. Here's a list of the basic tools you should have: an analog/digital multimeter, welding gun, desoldering station, and magnifier. These tools can resolve common problems such as shorts, broken wires, or faulty components.
How to test a board that stopped working?
Start with a visual inspection
When a circuit board suddenly stops working, there are sometimes obvious signs of a problem. You need to rely on your eyesight to spot defective components or signs of damage. Often, circuit boards deployed in the field are damaged by power surges and there are visible signs on the PCB.
Look for burnt spots, especially on power modules or I/O and connection ports. Watch out for cracked ICs, broken traces, and blown capacitors. Sometimes you can track down damaged components by their pungent smell.
Check the power module
If the components look good, you need to power up the board. Use a multimeter to measure the voltage on the power rails. Both the input and output of the regulator need to show expected values.
If the input voltage measured at the regulator is 0V, check the fuse. If the fuse is replaced and it opens immediately after power-up, it means other components are shorted and draw a lot of currents.
A voltage at 0V or below Vcc at the output usually means, a short circuit in the regulator or a component on the voltage rail. If this is the case, the damaged component will heat up quickly. Bring your hand close to the component to feel if too much heat is dissipating. Be careful not to touch the component directly while it is powered, as it can get very hot.
Remove the overheating element and verify that the voltage has returned to the expected value. If the observed voltage is still different from the expected voltage, there may be more components that have damaged the voltage wire.
If there are no signs of the parts overheating, look for signs of breakage. A broken trace may cause the voltage to be detected at some points of the trace but not at other points. Use a multimeter to narrow down the discontinuities.
Check input/output ports
I/O is also a common point of failure. Damage to an I/O port rarely shuts down an entire circuit, but usually causes a system malfunction. For example, an alarm controller that always senses an open door or a continuously activated motor, even if the door is closed.
If the I/Os are protected by fuses, Zener diodes, or varistors, make sure they work well. If so, the logic IC or microcontroller may be damaged. The only way to find out is to replace bad parts with good ones.
Check the communication port
Boards with communication ports such as Ethernet and RS485 have an increased risk of failure. When a communication failure is detected, check for burnt or cracked protective elements such as communication ICs or Zener diodes.
Optimize the board for troubleshooting
Circuit board testing is a tedious process, especially for issues like shorts. However, there are several ways you can optimize your PCB for future troubleshooting.
First, you can create test boards for voltages and critical signals such as communications. It saves you from trying not to mistakenly short adjacent traces with a multimeter probe.
It also helps to add LEDs as visual indicators of power, I/O, and communications. They help you zoom into problem areas with minimal detection.
These changes can be easily made with the right PCB design and analysis software. OrCAD constraint management rules ensure that test points are placed in strategic areas and are not erroneously hidden by components.
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