2008 Mac Pro Memory Riser Problem

[Essence_of_War]

My gf has a Mac Pro 3,1 (early 2008) and I think the upper memory riser has died. Is that a serious problem if she is able to use all of the RAM she needs without it?

She had 4x 2 GB RAM DIMMs, and 2x 1 GB DIMMs in it, and it was occasionally giving her blinking power light POST codes, and then she noticed that she only had 8 GB of RAM available.

I booted her Mac Pro in every combination of the DIMMs between the upper and lower riser that I could think of and I found that every DIMM pair was recognized if it was in the lower riser, no DIMM pair was recognized if it was in the upper riser, and if there was RAM only in the upper riser, it would not boot and give only the blinking power light post-code.

I left the top RAM riser in, removed the 2x 1 GB DIMMs, and placed the 4x2GB DIMMs in the lower riser, and she has not encountered a post-code since, and OSX always recognizes the full 8 GB of RAM.

Everything seems to suggest a dead riser, or maybe a dead riser connection, right? Will leaving the dead riser in cause any problems in the long-run? I know that technically having all 4 slots on the lower riser populated but no slots on the upper riser populated is not the correct configuration for a total of 4 DIMMs. The manual calls for 2 slots on each riser to be populated if there are 4 DIMMs, but if it boots and recognizes all of the RAM without trouble, I suppose the worst case scenario is just that it isn't operating in the maximum number of memory channels, right?

 

[DaveVandorAmon]

My gf has a Mac Pro 3,1 (early 2008) and I think the upper memory riser has died. Is that a serious problem if she is able to use all of the RAM she needs without it?

If she doesn't really need 10GB of memory, then no.

Everything seems to suggest a dead riser, or maybe a dead riser connection, right? Will leaving the dead riser in cause any problems in the long-run?

Did you swap riser cards to see if the problem was the riser board slot on the logic board, or just fully populate the working riser? A riser card is relatively inexpensive in comparison to replacing a logic board.

I know that technically having all 4 slots on the lower riser populated but no slots on the upper riser populated is not the correct configuration for a total of 4 DIMMs. The manual calls for 2 slots on each riser to be populated if there are 4 DIMMs, but if it boots and recognizes all of the RAM without trouble, I suppose the worst case scenario is just that it isn't operating in the maximum number of memory channels, right?

If it boots and works well enough, then you're A-OK to use it till you can replace the riser for best performance.

I would think the worst case scenario is this could be indicative of the machine heading out. I would probably run the Apple Diagnostics just to be sure.

If I recall correctly, it needs all 4 channels to achieve the maximum memory bandwidth.

You're down from 3/4 channels to 2/4 channels. It's funny though, to achieve the maximum b/w, you still hit a latency penalty from having 8 sticks, not to mention the heat and power draw.

Good luck. I would check eBay for a riser board after figuring out whether it's the riser slot on the logic board or the actual riser card. Riser cards are finicky as hell, having dealt with them on the HP tower servers, and Precision workstations for memory and second processors.

 

[Essence_of_War]

I would think the worst case scenario is this could be indicative of the machine heading out. I would probably run the Apple Diagnostics just to be sure.

I'm worried about that too. Tower was a graduation present, and she is very attached to it. Moreover, it would be financially tricky to replace it.

I don't think I tried swapping the riser cards actually...I'll do that tonight or tomorrow just to check. I poked around ebay, and it looks like the actual riser cards are pretty inexpensive to replace. *crosses fingers*