There are some text logs that are floating around in the folders of the OS, but if I had to guess, there is probably some issue with one of the gigabit ethernet transceivers that talk between the PCI interface card and the acquisition board. At least on my 7200 (non A) they use HDMP-1636A chips, several on the PCI card, one on the acquisition board, and two each on every ADC module, one for talking to the other ADCs, one for going directly back to the PCI card.
I'd check the color coded differential cables going between as a start, but the text logs could maybe point you to which one was an issue. Especially if it comes back with a reboot, it could be that some intermittent error just made it stop altogether for safety, instead of a dead chip or something.