would it be these caps that failed ?
https://www.cloudynights.com/uploads...136_thumb.jpeg
also any clue as to a realistic current demand for this device? just to narrow down an exact fix
At best guess the device seems to lack any reverse polarity protection, however It is unclear if the failure mode was over-voltage or reverse voltage
My first recommendation would be fit a fuse inline with the power, this will prevent things going poor with what I will suggest next
Reverse polarity case
- Option 1: Fit a P channel mosfet, reverse polarity protection circuit (mosfet, 1 resistor, 1 zener diode) and it will be as safe as houses, as the input is open circuit until it sees about +3V in most cases
- Option 2: Fit a large diode backwards across the power connection wires, any reverse polarity will blow the fuse
Over voltage case
- Recommended: The current regulators fail at 18V, replace the 2x AP1117 series linear voltage regulators with 1x R-785.0-0.5 for the 5V regulator and 1x R-783.3-0.5 for the 3.3V regulator, with this it would take up to 32V to fry the main regulators, some ceramic capacitors may fail before them, but that should not hurt the rest of the device if fused
- Option 1: Fit a TVS protection diode to act like a shunt regulator until the fuse blows if the supply voltage gets too high, e.g. something like a P6KE18A,
- Option 2: I can probably help tweak the reverse protection mosfet circuit to also open circuit the input when the supply voltage gets too high, tell me if you want to explore this option