A measurement across J17 Pin 1 and GND, as well as J17 Pin 2 and GND here at Logic show a voltage drop of ~2.7 V.

According to the i.MX31 schematic this is correct.

GND was measured from J17 - Pin 20 on the baseboard.

- andrewa@logicpd.com

Thanks, I've found the problem to be (faulty?) connectors between cpu board and baseboard. Everything works apart from JTAG. If I apply a lot of force, JTAG gets voltage and devices on the jtag chain can be seen. But as soon as pressure is no longer applied, the jtag disappears.

Seems I need to bolt the cpu board to the base board to get it working properly. I'm sure it's not supposed to be like this.

Your assumption is correct. The kit I tested did not have any mechanical connections aside from the electrical mating with the baseboard through J1 and J2

I will caution you in applying "a lot of force" to the SOM. Althogh the connectors are rigid, the PCB will flex, thus applying to much force may possibly break one or more solder joints with the the connectos.

Do you have access to a microscope or magnifying glass? If you do, I would check the current condition of the solder connections between the SOM and connectors J1 and J2, especially the pins assocated with the JTAG.

-andrewa@logicpd.com