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Generally there are three major reasons for semiconductor damage:
* overvoltage, even peaks in the low microseconds
* overcurrent.
* overtemperature (of chip)
The limiting values are given in the datasheet.
Hard to say what's the root problem with your circuit, without knowing schematic, voltages, currents..
If the burnt thing was the power supply input to the board (probably not), accidental reverse polarity can be a problem that burns boards. Using the 'wrong' adapter (e.g., a wall plug-in AC in and DC 5V or 12V out type) which has a barrel jack male that has + and - inverted to the board barrel jack female + and - connections (inner and outer ring) is a good way of burning boards or seeing smoke first and disconnecting before major damage is done if lucky. Always check the picture on the plug/adapter and on the device before using to ensure they match polarity orientation, or test adapter barrel jack with DMM voltmeter.
If the burnt thing was the power supply input to the board (probably not), accidental reverse polarity can be a problem that burns boards. Using the 'wrong' adapter (e.g., a wall plug-in AC in and DC 5V or 12V out type) which has a barrel jack male that has + and - inverted to the board barrel jack female + and - connections (inner and outer ring) is a good way of burning boards or seeing smoke first and disconnecting before major damage is done if lucky. Always check the picture on the plug/adapter and on the device before using to ensure they match polarity orientation, or test adapter barrel jack with DMM voltmeter.
I have checked both power supply board and pneumatic board, then I found pneumatic board was defective.
After replaced new pneumatic board, burning problem has been resolved. Now device is working well.
Just i would like to know the reason for burning this particular component.
If the design is any indication, the concerned item is most likely a transistor. There are very similar ones (appearances can be deceptive) in the neighborhood but they are intact. Voltage spike will damage the semiconductor but the package will be not affected. The device must be producing lots of heat, most likely from over current for some extended time. The casing is plastic (molded epoxy resin) and it must have got hotter than 200C. The transistor is connected to a load and there is most likely a fault there.
To debug, look downstream the problem. Why the particular component was overloaded?
Was the load some kind of a sensor? It looks like an array of loads in parallel.
If the design is any indication, the concerned item is most likely a transistor. There are very similar ones (appearances can be deceptive) in the neighborhood but they are intact.
You give good advice about looking for the cause downstream, etc. I don't want to be contrary, just so you understand. Something I mave my doubts about is thinking the blown part is a(nother) transistor because all the others have two resistors coming off them in an identical pattern and no capacitor but the blown part has no resistors (or so it appears) and what looks like a capacitor next to it. I wonder what it was.
You didn't give sufficient information. At least, you should post a detail photo of the new board allowing identification of the component of interest. Also a board bottom view showing the external connectors. Also - if available - additional information like schematics or block diagrams from the service manual to understand the board function and role of the defective component.
is it a two pin component? To me it looks like its a capacitor which got damaged/shorted e.g. due to mechanical stress as the mounting hole is in its vicinity. Is it possible that there are two capacitors in parallel, one can be seen below the destroyed component. Please clean the failure area to allow a clearer view.
FYI, there are so called Open Mode/Fail-Safe (MLCC) Multilayer Ceramic Capacitors, which should help to avoid short-circuit failures caused by mechanical stress.
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