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A couple of problem EMX modules


From our last batch of 20 boards there were a couple that didn’t pass test and were put aside. I spent yesterday fault-finding them, one I’ve patched to get working but the other still has a problem.

Board 1. SD Card Power Problem
The board complained of “No SD Card”, and it turned out that SD_PWR (EMX pin 68) was only supplying 0.5V rather than 3.3V. The line wasn’t shorted to anything, and when powered down showed the same impedance to ground as other working boards. I cut the track and connected the SD power line to the 3.3V rail, and the SD card is now functioning correctly. The now unconnected SD_PWR line from the EMX still only shows 0.5V.
All functions on this board are now working

Board 2. USB Device Fault
As our application works as a USB device, we use the COM port for loading and debugging, although we have a jumper on LMODE so we can switch to USB debugging if required.
(Gus - Would it be possible for the GHI updater to give us the option to use the COM port?)
When this particular board was connected, the PC would report that the device had a USB fault. Same message when jumpered for USB debug and booted TinyBooter or GHI Loader mode.
Checking out the UD_D+/UD_D- lines, no shorts, impedance the same as on working boards. Looking at the D+/D- lines on the CRO, D+ was ok but D- was hardly budging from 0V. I traced the line back as far as R20 on the EMX module, which checks out at 33 Ohms, same as on the other boards, before it dives into the unknown depths of the module. The connections look fine under the microscope. I can only surmise that there is an open circuit or other problem somewhere on the EMX module itself.
I welcome any suggestions on how to proceed now.
(All functions on this board except USB are working correctly)



I wonder if the module was overheated when placed.

The new tool supports serial update of the firmware.


I guess it is possible, but unlikely. All the boards go through the oven on the same heatup profile, peaking at 250C, as per the EMX reflow spec.
It hasn’t been reworked at all. (The rework air is set at 340C, but there’s never a need to rework the module itself)

Thanks Gus, I’ve found it now. I had seen the “FEZ Config” tool before, but I think of my board as an “EMX”, not a “FEZ”, and it didn’t register as applicable.