Mac Pro 5,1 weird RAM issue

pastrychef

macrumors 601
Original poster
Sep 15, 2006
4,520
1,020
New York City, NY
I have a Mac Pro 5,1 with a pair 8GB sticks of RAM (16GB total). I decided to add another pair of 8GB sticks. When I installed the RAM in slots 1, 2, 5, and 6, the red light for slot 6 on the riser card lit up and the system only saw 24GB total.

When I installed the RAM in slots 1, 2, 3, and 5, all 32GB was seen and no red lights.

When I installed the RAM in slots 1, 3, 5, and 7, all 32GB was see and no red lights.

When I installed six 1GB sticks in slots 1, 2, 3, 5, 6, and 7, all 6GB was seen and no red lights.

When I Installed four 1GB sticks in slots 1, 2, 5, and 6, all 4GB was seen and no red lights.

Is this behavior normal? Have any other Mac Pro 4,1 or 5,1 users experienced this? Thanks.
 

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cal6n

macrumors 68000
Jul 25, 2004
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24
Gloucester, UK
I believe the problem is usually associated with incorrectly fitted processor upgrades. Is your Mac Pro stock or upgraded?
 

pastrychef

macrumors 601
Original poster
Sep 15, 2006
4,520
1,020
New York City, NY
I checked all the pins with a magnifying glass and all looked good. I also swapped the position of the two CPUs. Nothing changed. All symptoms remain the same.

The oddest part is that when I try with 1GB sticks of RAM, everything works as it should.
 

cal6n

macrumors 68000
Jul 25, 2004
1,935
24
Gloucester, UK
That might be your problem.

I may be wrong, but I thought that the 5,1 dual would only take the later westmere 56XX processors.

It's mentioned (but not explained) in the first post of this thread.

What were your original processor numbers?
 

pastrychef

macrumors 601
Original poster
Sep 15, 2006
4,520
1,020
New York City, NY
Originals were E5420s. My assumption was that since 4,1 models could be upgraded to 5,1 models with a firmware flash and were able to run X5570s fine, a machine that started off as a 5,1 would not have problems either. Again, this was just my assumption and I could be way off the mark and totally wrong...
 

cal6n

macrumors 68000
Jul 25, 2004
1,935
24
Gloucester, UK
Yeah, that's what I thought.

Anyway, it's not an unreasonable assumption that you've made but it may not be true, unfortunately. If you've still got your 5620s, you could try swapping them in with your new RAM to help zero in on your problem.

I suspect you'll need the later processors for your machine to avoid glitches, though.

Here's a list of the whole family.
 

pastrychef

macrumors 601
Original poster
Sep 15, 2006
4,520
1,020
New York City, NY
Unfortunately, the original CPUs are long gone. I sold them after installing the X5570s and ended up profiting from the upgrade.

I am beginning to suspect the RAM modules that I have installed. I have four sticks of these Kingstons.

I think I've exhausted all reasonable testing measures and I think I will just leave well enough alone for now. Thanks for all the help.
 

jsanford

macrumors newbie
Aug 26, 2013
2
0
did you ever find an answer to this issue?

Did you ever find an answer to this? I am experiencing the same thing.