My tinyg was working until about an hour ago. the drv8818 on motor 2 has a small crater in it. immediately prior I had been driving the Nema 23 steppers with a battery drill with the tinyg power off and noticed that it powered on, booted up and the serial came to life. the next attempt to power and use the tinyg board saw motor 2 driver getting very hot and the bench power supply limiting current at about 2 amps.
I am going to try to replace the drv8818 chip.
Any chance that the stepper back drive was the drv killer?
Manually moving the gantry on a belt CNC (e.g. Shapeoko) will cause tinyG lights to blink, etc, due to back drive, but no one has reported a death such as this.
But, it would not surprise me that constant drive such as you had, for a period of time, could likely have exceeded the tinyG input voltage .
I suggest you read the 8818 product data sheet.
It is a heat slug pachage, soldered to the PCB.
You are going to need a lot of heat and 3 or four hands (or good fixturing)
I was able to remove the 8818 and the other 3 channels still work fine (lots of heat required!) I have a few replacement chips on order, i'll let you know how the replacement goes.
just for grins i drove an unconnected stepper thru a resistor and diode and it makes quite a generator.. upwards of 60v! no more backdriving.