Resolved 2006 Pro RAM issues

[AL1630]

I recently picked up a 2006 Pro (2.66), and the bottom RAM slot seems to not work. It has 8GB of RAM, 2 4GB modules. If I put both modules on one riser and mount it in the top slot, OS X recognizes all 8GB. However, if I have one on the top and one on the bottom, only 4 GB is recognized, and if both are on the bottom, it won't boot. I have tested both risers and they both work, but ONLY in the top slot. Is the slot dead, or is the RAM installed wrong, etc.?

 

[OS6-OSX]

http://manuals.ramjet.com/MacPro_MemoryDIMM_DIY.pdf

 

[AL1630]

Thanks for the link, it'll probably be useful in the future! So the way the ram is configured, if I bought 2 more modules, they would have to be installed in the lower riser?