Mac Pro 3,1 memory riser board issues...or what?

[inezhs]

I just got my Early 2008 Mac Pro 3,1 running again by replacing the power supply. It was dead about 3 years. It currently has 4GB RAM, but on boot I found I was only getting 2GB. What worked instantly to give me 4GB was to place the dimms so: A1, B1, A3, B3. Now I'm planning to add 2x4GB dimms for a total of 12GB. Problem is, it seems somehow that A2, B2, A4, and B4 are all dead? I can't quite figure out how these matching slots died simultaneously on both riser boards. These are the configurations I tried to test the slot:

A1, B1, A2: ONLY A1 & B1 WORKED FOR 2GB
A1, B1, B2: ONLY A1 & B1 WORKED FOR 2GB
A1, B1, A3: 3GB
A1, B1, B3: 3GB
A1, B1, A4: ONLY A1 & B1 WORKED FOR 2GB
A1, B1, B4: ONLY A1 & B1 WORKED FOR 2GB
A1, B1, A3, B4: ONLY A1, B1, A3 WORKED FOR 3GB
A1, B1, B3, A4: ONLY A1, B1, B3 WORKED FOR 3GB
A1, B1, A2, B3: ONLY A1, B1, B3 WORKED FOR 3GB
A1, B1, B2, A3: ONLY A1, B1, A3 WORKED FOR 3GB

So are both riser boards bad or could it be something else? And, yes, I'm stuck upgrading this ancient Mac.

Also, I'm seeing 3 different riser board part numbers that supposedly work on my Mac: 922-8492, 820-2178-A (the type I have) and 630-8751. Is this correct?

 

[OS6-OSX]

http://www.macpartsonline.com/mac-pro-parts/mac-pro-early-2008-a1186-parts.html?p=1
https://www.macpartstore.com/index.php?p=catalog&mode=search&search_str=630-8751
https://www.macpartstore.com/index.php?p=catalog&mode=search&search_str=922-8492
https://www.macpalace.com/index.php?p=catalog&mode=search&search_str=922-8492
https://www.macpalace.com/index.php?p=catalog&mode=search&search_str=630-8751
https://www.dvwarehouse.com/index.p...sult&search_in_description=1&keyword=922-8492

 

[inezhs]

Yes, I understand configuration, but I was testing the riser board slots with the 4 dimms that I have. They show up in System Profiler as OK and the dimm type or as Empty. The only way I've gotten my entire 4x1GB dimms to show up and give me a total of 4 GB is placing them in A1-B1, A3-B3 (according to System Profiler).

It is just very hard to believe that the same 2 slot on each board has gone bad, A2, A4, B2 and B4, but these show up as empty when tested. Can there be some other problem besides both boards being bad?

The above is the only configuration that gives me my entire 4x1GB ram.

Also, the original riser boards I have show part number 820-2178-A. But, I guess those other work...

 

[inezhs]

OK, my bad. I had my ram manufacturers mixed up even though the dimms have the same specs. Now I can see slots A2 and B2 are working. Trying to figure out now how to test slots A4 and B4 with only my 4 dimms. *sighs*
[doublepost=1549492998][/doublepost]I figured it out! If I insert all 4 dimms, paired by manufacturer, in the top riser board they all show up in System Profiler. I did this on each board, swapping them out to the top. ALL MY SLOTS WORK! YAY!