FEZ Cobra broken?


I have FEZ Cobra board. I might have connected sth inproperly (GND, power, etc.) and now FEZ Cobra is not communicating fully with PC via USB.
MF Deploy does not see device.
Red power LED is on and yellow LAN LED is on.
If I connect to PC GHI Boot Loader Interface is visible in Device Manager.

I can upgrade firmware:
– Log –
Connecting to device…
EMX found at Port#: COM47
GHI Bootloader Version: 1.02

Device will be updated automatically! DO NOT disconnect or turn off the device!
Erase successful!
Updating TinyBooter. Please wait…
Update successful!
Disconnecting COM47
No response from device

But then nothing happens. I cannot communicate with a board using MF Deploy nor Microsoft Visual.

What can I do to bring it back to life?

Thanks in advance,


Try manual firmware update please

Further to that, please also take screenshots of Device Manager to show us what is visible after the firmware update, and then use MFDeploy and see if you can detect the correct device. I’d also suggest swapping USB cables as a low-value-but-easy-to-try step that might make a difference.

Guys, thanks for helping, but still no success.

  1. I have changed cable.

  2. I have done manual update, but here I see small issues. Steps I am performing:

2.1 Plug FEZ Cobra with another USB cable to PC (not holding any buttons on the board). Yellow LAN and Red Power LEDs are ON. Here is the Device Manager (dev1.png, dev2.png). GHI Bootloader Interface on COM4 is recognized.

2.2 I am launching manual firmware update using http://www.ghielectronics.com/downloads/general/teraterm_utf8-4.53.zip.
Output in tera.png.

And here is issue, because manual says “Once loading has finished and the file is valid, the new firmware is executed automatically and you will not see BL again If you did see the “BL” again after this process, it means that the update process failed.”

But I see BL and new firmware is not running and there is no change in Device Manager.

I still suspect that sth was broken when I have wrongly connected GND, 3,3V OUT, RTC BAT pins, where 12 V could have been connected.

Is there sth else I can do ?


Jacek Dobrowolski

If you connected 12V on the 3V3 pin, then there’s a big chance you lost the Cobra forever. Still strange that you can update the bootloader though.

Well, I would say, that I can access bootloader, and try to update, but it seems that it is not successful.

Please help…

Do You think that sth has broken and can be replaced on a board?
Or EMX is partly damaged?


I agree with you Jacek that it’s strange you can get into the bootloader but can’t deploy. It may be that the processor has corrupted it’s flash in some way, or there’s some other problem with the processor actually starting anything other than the bootloader. Gus might be along and offer some thoughts on what might cause this. If this is true then the likely only replaceable component is actually the EMX board, it’s unlikely you’d be able to repair anything on the EMX module itself.

Indeed, no schematics for EMX board itself. And even replacing the EMX module will be a hell of a job. With a hotair gun, you will blow away other components. The only solution I see is to put the board on a hotplate and carefully remove the EMX module, but this will also lift all through hole components like ethernet and DC connectors.

This case reminds me of my FOX board, I once connected 12V to the 5V input. Thereafter it was also booting, but after that it hung and all I/O’s began to resonate. Just saying that nothing is what it seems after you’ve applied the wrong voltage. You only need to blow up a single transistor in the chip to make it doing crazy stuff as each transistor in there is actually needed.

BTW: how are you powering the board now? If it’s by USB or DC adapter, can you measure the output of the 3V3 regulator with a oscilloscope to check if it’s still stable?

I will check that, but It would be strange if bootloader works, if power supply is wrong…

Actually it seems that I have connected 12V to GND…

So you just shorted the power supply? Or was the other end connected to an other pin?

I have connected external 12V to GND.

So do you really mean you’ve just reversed the polarity, or did you have 5v connected and then connected 12v to GND?

If you just reversed the polarity, ie connected your power supply’s12v to GND on your Cobra and the power suppply GND to the + rail, then you may not have damaged anything/much, but you should check the VREG output as Wouter says; you may have to look at the circuit diagram though to make sure that there are protection diodes there too.

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