Just checking - fried Spark

I’m building an RFID reader using a great little board from Priority1 Design. This board provides me with regulated 3v3, which I drop into the top-right pin on the Core ( VCC / pin 24 / labelled 3v3 on the board ). The RFID board and the Core share a Ground. It then communicates to the Core over serial, the pin labelled RX on the Core. We’ve tested this for several days, during which they happily work together and the Core sends me RFID data over the Cloud. All in all, it seems to be great.

Yesterday, however, it seems like the Core fried. This wasn’t during “standard use” - I’d given it to others to scan some RFID tags, and I’m not quite sure what they did with it, but the Core currently doesn’t light up when rebooted or plugged in directly over USB, and just gets very hot. My solder looks like it’s holding fine and I can’t see any short-circuits.

Any thoughts on what may have fried the Core ? There’s a small chance it somehow fried when it was disconnected from its power supply and then plugged in over USB to diagnose what was going wrong, but from what I understand, it was already not booting after being power-cycled through the RFID board - that is, it stopped reading, so they unplugged the power supply at the wall and plugged it back in. Again, the power supply provided to the Core into Vcc is 3v3 regulated, from the RFID board, which we feed with a 12V wall wart. If anyone’s interested, it’s this beast - http://www.priority1design.com.au/rfidrw-e-ttl.pdf

Any thoughts, advice, opinions appreciated. Thanks !

What part of the Core is getting very hot when powered via USB?

Is it the regulator? Or is it the µC itself?

Does it show any LED activity when trying to perform a factory reset?

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No LED activity when being powered, no response to a system reset. It looks to be the WiFi module that’s getting very hot.

The Core is currently still soldered down to a perfboard, so I only have access to the top until I get around to removing it. The WiFi module is heating up significantly ( and that might be the microprocessor underneath ), but the hottest part is whatever’s above the Vin pin, top-left. Thanks.

I guess you are talking about the protection diode between the USB connector and the Vin pin.
This could well have been damaged and hence powering via USB might fail due to that (haven’t checked the circuit diagram tho’ :blush:).

Have you checked how hot the USB connector gets? Since this is used as a heat sink for the 3V3 regulator directly underneath it, if this gets hot, your regulator might be damaged, too.
This sometimes happens when your power supply provides no really clean DC, even if the 5V/3.3V are not exceeded due to possible oscillations/resonances.

Another test is to measure the voltages on the Vin, 3V3 and 3V3* pins, when powering via USB (5V) / Vin (3.6-5V - don’t go to the upper limit ;-)) / 3V3 (3.3V !).

Keep your test short to avoid unneccessary heat strain on your components