An old story but true as I have seen it several times revolves around a defective bunch of Electrolytic s that Motorola used Many years ago... They were used in an old old black and white TV set and had a Very bad issue with exploding. The TV cabinets were made of a pressed, epoxied paper or wood product and when this particular filter "went off" it neatly punched a regular hole on the top of the case and then buried itself in the ceiling. I know of one that happened in a home and one in my TV shop (1963) and one in a shop I knew of a year or so later. And Yes Tantalum's are quite amusing/frightening when they are abused... Not too tolerant of simple abuse At All...
Was that smd uno powered via usb? Even with proper resistors on my leds on my older laptop the voltage will actually drop quite low, so low some leds wouldn't even light, I had to add a 4700uf cap to have them work properly without futzing with the arduinos own needs
No; it was a 9V battery through the power-in jack. I arranged the LEDs in a modern abacus style, and display numbers 0-99. I used an elastic band to tied the Arduino, battery, and breadboard to a ping pong racket, then I put it in the cool room in my basement. After 30 minutes, I went down to check the temperature. I turned on the Arduino, and it said that it was 15 degrees C. About 2-5 LEDs would light up at the same time (e.g. "15" used 2 LEDs). I usually don't turn on the Arduino with battery power for more than 60 seconds or so.