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This is a very subtle issue; if not careful, when connecting the oscilloscope, it can cause certain chips on the circuit board to suddenly explode (it really can explode!). This not only has a significant impact on the project but can also leave us feeling quite frustrated for several days. Therefore, it should be taken seriously by circuit designers and debugging personnel.
I have repeatedly fallen into this trap, and here I want to focus on analyzing the process of how I overlooked this hazard and suffered losses because of it. This point is crucial; because I did not pay attention, I suffered deeply. As for the solution, experts on forums (like the 21ic forum, which is quite confident!) have already analyzed it clearly.
The first time I fell into this trap was six years ago during a project involving a phase voltmeter. At that time, I was only responsible for microcontroller software programming. When the hardware designer connected the oscilloscope clips, a chip exploded. That designer spent two days fixing it and told me it was caused by a short circuit between the emulator and the board. As long as it powered on without delaying the debugging program, I didn’t pay attention. So, I carelessly overlooked this issue.
Later, I also engaged in hardware development, and there had been no further incidents during oscilloscope debugging. I used various oscilloscopes, including analog, digital, imported ones like Tektronix, and domestic ones as well. Several projects went smoothly until a few days ago when another chip explosion occurred, resulting in significant losses: first, the MSP emulator burned out. After replacing the emulator, I found I could not download programs to the MSP430F169, and even the USB port of my newly purchased laptop burned out. This time, I was using a domestic oscilloscope from Uni-T. This not only reminded me of the chip explosion incident six years ago, but it was likely the same issue. So where exactly is the problem? The same board had no explosions when debugging with a Tektronix oscilloscope, but if there is an issue with the Uni-T oscilloscope, I had already completed a project with that company’s oscilloscope, which had a measurement accuracy of five-thousandths level. I had a pretty good impression of this domestic oscilloscope and was quite proud of it.
Thus, I was frustrated for several days, suspecting everything from the circuit board to the quality of components, until I finally doubted whether the oscilloscope’s ground wire was shorted with the oscilloscope’s probe clips. I measured it with a multimeter, and indeed there was a short circuit. I suddenly understood—some chips on the board had high voltage entering the ground through the oscilloscope’s clips; it would be abnormal if they didn’t explode. I also searched online for ‘oscilloscope ground wire’; there are many related forums, and they have explained it very clearly. It left me speechless. This impression is extremely profound; perhaps this issue should have been clarified six years ago, but at that time, I carelessly overlooked it and really believed it was caused by a short circuit between the emulator and the board, leading to the current losses. Well, at least it was just a burned board; I heard someone online even burned down a piece of equipment in a running substation. If I had encountered such a situation, it would have been even worse.
In fact, we in design, including those in various technical fields, should have a mindset like this—being meticulous and careful, never overlooking any small problems we encounter. If we encounter one, we must work hard to resolve it. This is also what my mentor often reminded me: don’t skirt around problems; face them head-on. Now I can face my mentor, but unfortunately, I didn’t take it seriously back then. Perhaps it was due to youthful arrogance, or perhaps because I wasn’t independently managing projects and didn’t feel my responsibility, or maybe it was because he was the chief engineer and I was just a small soldier, and I couldn’t accept his attitude. Oh well, it’s all in the past. The only thing is, I am still very grateful to him. He is my mentor, and he has many admirable qualities that have allowed him to become the CEO of a company with 200 employees. I heard he is now driving a big Benz, which is well-deserved; I wish him well. I digress; let’s get back to the topic of grounding. To avoid voltage leakage and exploding components on the board, there are four methods: 1. Leave the oscilloscope power ground wire unconnected; 2. Isolate the oscilloscope power supply with an isolation transformer; 3. Purchase differential input probes; 4. Power the board with an isolation transformer.
Ultimately, the key is to ensure that the places where the probe clips are attached to the board do not have high voltage, ensuring safety. The best habit is to measure with a multimeter before attaching clips. Now, let me analyze my unresolved mystery.
Why didn’t the board explode when using the Tektronix oscilloscope, but now it smokes heavily with the Uni-T oscilloscope? Could it be that the Tektronix probe clips were not connected to the power ground, or was the Tektronix power supply isolated? I specifically called a colleague from my former company to measure it, and the Tektronix clips were indeed connected to the power ground. So why? Suddenly, I remembered that the power supply on our test bench at that time was pulled over with a two-wire power cord that did not have a ground wire. So why, when I used the Uni-T oscilloscope for the original five-thousandths project, did nothing explode even though the oscilloscope’s power supply was connected to the ground? Now I realize that the power supply for the five-thousandths project used a switch-mode power supply, which has isolation functions, hence it was safe. Looking back, I still feel a bit scared. The project had a very tight deadline, and it was my first project at the new company. If an abnormal incident occurred, it would have had a significant impact on me.
Alright, I’ll stop here. Perhaps some colleagues are already aware of this issue and might say that one should read the manual more or browse online for additional information; maybe some colleagues are still in the same state I used to be, waiting for disaster. I hope this can be helpful to everyone because using an oscilloscope is too important for us.
If everyone can safely use the oscilloscope, this is just one of the purposes of writing this article. Another important purpose is to hope everyone can develop a good habit that my former mentor required of me—don’t skirt around problems; face them head-on. Cultivating this habit is very challenging; it requires the courage to overcome oneself and the determination to conquer one’s laziness and carelessness. If we can have this habit, we can achieve a relatively perfect project, a technician can progress without taking detours, a life can lead to success, and a nation can remain excellent forever.
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