unbrick a devkit?

[papillon]

I have been uploading different samples to one of the ESP-WROOM-32 devkits we purchased a few weeks ago and up until today everything worked fine. Today, however, the devkit appears unresponsive: connecting it to the PC does not create /dev/ttyUSB0 as it always did. The red LED does light up and the ESP32 module heats up (as expected), but the PC does not recognize the device. After a while, I notice that the LED flickers somewhat, but it does not change the problem. I tried connecting a different devKit and that works as expected, so the problem is not the PC, but rather the actual devkit device.

further troubleshooting using

udevadm monitor

confirms that the second unit (the working one) generates "add" and "remove" events, but the first one (bricked?) does not. Pressing the EN an/or BOOT buttons does not change anything. lsusb does not list the device either.

So is there a way to un-brick this? Or further troubleshoot this without probes or scopes?
thanks for your help!

setup: Linux aisen 4.9.8-1-ARCH #1 SMP PREEMPT Mon Feb 6 12:59:40 CET 2017 x86_64 GNU/Linux

[ESP_Sprite]

Can you try to connect it and post the last lines of output of the dmesg command? Also, have you tried with a different cable?

[papillon]

thanks for the reply, but dmesg does not report anything.
No events from udev or from the kernel. It's as though the UART is stuck in a state and can't/won't communicate with the host pc

[ESP_Sprite]

'does not report anything' - you mean that the log is exactly the same before and after plugging in the board? Also, what specific devkit do you have?

If anything, the problem seems to be somewhere in the communication of the USB-serial chip and the PC, but you probably already deduced that yourself.

[papillon]

the dmesg output was indeed the same as before the USB cable was plugged in.
I say "WAS" because today, after spending the night unplugged, the device is working normally again. Looks like the hardware gnomes were hard at work last night
thanks for the help troubleshooting this.
FYI: ESP32_Core_board_V2

[ESP_Sprite]

Strange, maybe an USB hickup or a flakey solder joint somewhere. Hope it was a fluke.