I’ve got an M404 that was running just fine for 18days (433hrs on the dot), but now it won’t boot or get recognized as a usb device. I’ve tried it on the Particle breakout board as well as a few of the same PCB it was installed in. The original power supplies seem to be just fine as well providing 3.3v & 4v within a few mV.
Not sure if there is a way to do any diagnostics on it? I think I have a JTAG interface here somewhere if that’s an option.
Some possibilities include:
Software is causing the device to sleep immediately. If you have the status LED populated or use the breakout board, the LED will probably do a single white blink at boot. If you hold down the MODE button while applying power, it will probably go into safe mode or DFU mode.
The bootloader is corrupted. The LED won't come on, and the buttons won't respond. The only way to tell if this is happening is to use a SWD/JTAG debugger. On the M404 you have to be careful because there are 3 bootloaders and if you flash prebootloader-mbr or erase the flash it will no longer be able to be restored because there are unique secure boot encryption keys.
There is a hardware failure.
Well I tried to flash the bootloader following the instructions per the docs using J-link lite to do the flashing work but it couldn’t even identify the device. I tried the same steps with a brand new M404 and it connected/flashed each part just fine.
Is there any way to determine what the hardware failure is and how to prevent it in the future? I’m planning on having 10 or so of these installed in remote locations in the next year. I could try to rip the cans off the board I suppose but it doesn’t have the burnt electronics smell to it…
Edit: Forgot to mention, the status LED definitely does not work.
It's not clear what failed or why. It's not a common failure, but as with any electronic component it could fail.
Since the MCU does not appear to be functional (JTAG does not work), two possible causes are an issue with the 3V3 rail, like a voltage spike, or generic issues like ESD. The RTL872x is fairly sensitive to its power; things like improper slew rate will prevent it from booting, but should not damage it.
I suppose I’ll roll with ESD of some kind since it is in a plastic enclosure outdoors. I’ll look into methods to help prevent static buildup and hopefully it won’t happen again.
I appreciate the help!