O/C Mastercard - P2 auxiliary connector

Shaun,

While the board is disconnected from both USBMaster and External Power please
check that all pins on U3 have connectivity to where they should.
Use the Ohm-meter and test between U3 – pin 1, 2, 3, 8, 13, 15 & 16
and the same pins on U4 (1 to 1, 2 to 2. etc.). The last to test is U4 pin 14 to U1 pin 7.
Then add your External Power and measure that you have +5V between pin 16 and pin 8 (GND) on U3.
If all OK then add your Expansion and see what's happen.

BTW - Have you verified your DB25 cable between Master and Expansion?

Just so I have the pin numbering right for U3 and U4;

When looking at the back of the mastercard with the P2 and DB25 ports facing up, Pin 1 would be top row furthest right and Pin 9 bottom row furthest right?

EDITED:

Got it working. While really checking out the pins on the chips, I discovered a barely visible piece of solder bridging two pin on U3 between the chip and the P2 port. Once I broke that connection, everything is working perfectly now (so far).

Thanks Perik for all your help!

Great Shaun,

As I said - "I'm sure you will succeed"

I don't know how OC do their testing of pre-build cards but this is not good!!
and not the first time:(. Nice thing though about OC hardware is that you usually can
"walk" into the circuit board. That’s not the case on some of the new hardware
options where a Microscope is a must;).

Nice to able to give some "remote" help.