I made a PCB with two Arduino Pro Micro 5V on it as a control system for a machine. The PCB is powered by a 24VDC PSU and a part of that 24 VDC goes to a R-78C12-1.0 DC-DC converter. That gives 12VDC 1A to the RAW pin of the pro micro.
It worked perfectly for few weeks but one day the Arduinos randomly fried itself when I powered the machine/PSU on. The voltage regulator was the part that was damaged. I couldn’t figure out what caused it.
I used a spare PCB and since the second Arduino isn’t important/needed for now, I only used the one Arduino. I also placed a polarized capacitor between the 12VDC DC-DC Converter and GND. I did this thinking it will stabilize the 12 VDC going into the RAW pin. Now when I turn it on it works sometimes, other times the HR-SC04 Sensor and LCD screen don’t work and I noticed the VCC pin on the Arduino dropped to 2.8V. When it was having this problem, I tried to connect a micro-USB cable in and that caused the Arduino to fry again. It was the voltage regulator again that was burned and blackened.
I looked online to see if others had similar problem and couldn’t get an answer. The only option I can see right now is to get a DC-DC Converter that output 6.5V instead of 12. Attached a screenshot of the schematics I’ve drawn on the easyEDA software.
Would anyone have any idea what caused this fry up? Schematic of the PCB The PCB where the Arduino Pro Micros burned out Close up of the voltage regulator. It says "4BMD" on it before it was blackened. The PCB mounted on the machine.There is plastic spacers so there isn't electrical contact between the sheet metal and the PCB.