Precision T1700 memory failure

I am getting the 1-3-2 beep on startup in my Precision T1700.  I had four different sticks of memory in the system when the problem began.  I have tried taking out all but one of the sticks, leaving a single stick in slot 1, for all four sticks.  The 1-3-2 beep happens in all cases.  It feels unlikely to me that all four sticks failed simultaneously, and therefore the problem is likely the motherboard despite the memory failure error message.

Is there anything more I can do to narrow down the issue or confirm my hypothesis before I go in search of a replacement motherboard?