Resolved DIMM Slot 1 Not Recognized after CPU Upgrade

msh

macrumors 6502
Original poster
Jun 13, 2009
331
107
SoCal
I just successfully upgraded to a X5670 6 core CPU but now DIMM slot 1 has red led and not recognized. Dimm slot 2 is fine. I swapped the 16GB 1333 DIMMs between slots and still slot 1 not recognized so doesn't seem to be a problem with the DIMMs. However, If I put the DIMMS in slots 2 & 3, no problem. What could be the issue with slot 1?
 
Last edited:

estabya

macrumors 6502
Jun 28, 2014
430
352
I would guess a bent pin. You might pull the CPU back out and take a look.
 

h9826790

macrumors G5
Apr 3, 2014
12,766
5,577
Hong Kong
That could be but I am wondering whether it may be that the bolts are not tightened enough or evenly enough.
Not quite possible for single processor cMP. The socket itself should lock the CPU into the perfect position. Heatsink pressure is more for cooling performance.
 

msh

macrumors 6502
Original poster
Jun 13, 2009
331
107
SoCal
I’d remove the cpu and check the pins in the socket and put it back together.
I removed the CPU, examined with a strong magnifying glass and neither socket nor CPU shows any bent pins or damage whatsoever. I have reassembled and I appear to have full functionality with exception of dimm slot 1. I could live with that until I want to add more memory which I don't right now but like to have that option. I note that I have used an anti-static wrist strap and have unplugged the MP prior to every removal of the CPU tray. So am I to conclude that the CPU is defective (perhaps prior ESD damage?)?
 

tsialex

macrumors 603
Jun 13, 2016
5,298
6,019
Brazil
I removed the CPU, examined with a strong magnifying glass and neither socket nor CPU shows any bent pins or damage whatsoever. I have reassembled and I appear to have full functionality with exception of dimm slot 1. I could live with that until I want to add more memory which I don't right now but like to have that option. I note that I have used an anti-static wrist strap and have unplugged the MP prior to every removal of the CPU tray. So am I to conclude that the CPU is defective (perhaps prior ESD damage?)?
Install your original Xeon and test if you have the DIMM slot working. If it works again, your new Xeon is defective.
 

msh

macrumors 6502
Original poster
Jun 13, 2009
331
107
SoCal
Install your original Xeon and test if you have the DIMM slot working. If it works again, your new Xeon is defective.
Yes, I will do that. FWIW, I have hyper-threading turned off - that shouldn't make any difference should it?
 

msh

macrumors 6502
Original poster
Jun 13, 2009
331
107
SoCal
How do I do that?
I know how to do a command-option-p-r once but what is sequence for three times in a row? Do an immediate shutdown after the first two or just keep holding the keys down on the first one and it repeats itself twice?
 

tsialex

macrumors 603
Jun 13, 2016
5,298
6,019
Brazil
I know how to do a command-option-p-r once but what is sequence for three times in a row? Do an immediate shutdown after the first two or just keep holding the keys down on the first one and it repeats itself twice?
3 clear NVRAM process in sequence, so you keep pressing the keys until you completed it 3 times.
 

msh

macrumors 6502
Original poster
Jun 13, 2009
331
107
SoCal
Thank you Alex.
[doublepost=1561061383][/doublepost]
Not quite possible for single processor cMP. The socket itself should lock the CPU into the perfect position. Heatsink pressure is more for cooling performance.
That being the case why all the dire warnings over over tightening the heatsink?
 
Last edited:

pl1984

Suspended
Oct 31, 2017
2,230
2,603
That being the case why all the dire warnings over over tightening the heatsink?
This only applies to the dual CPU 4,1 Mac Pro as they use delidded CPUs. The single CPU 4,1 and all 5,1 models use lidded CPUs thus you generally do not have to worry about the height.
 
  • Like
Reactions: h9826790

msh

macrumors 6502
Original poster
Jun 13, 2009
331
107
SoCal
Probably not, but clear NVRAM three times to force the DIMM re-detection process.
This did not solve the slot 1 problem; it did re-enable hyper-threading though. I will put the old cpu back in and confirm that the socket is still good.
 

msh

macrumors 6502
Original poster
Jun 13, 2009
331
107
SoCal
I found the problem. It was bent pins in the socket. Very subtle and difficult to see - only visible by reflected light from an angle. I knew when the old CPU had the same problem it had to be the socket and so I took a closer look. I must have bent them when removing the old cpu at an angle. I bent them back with a dental pick. All normal (and faster) now.

Appreciate all the help.
 
Last edited:

msh

macrumors 6502
Original poster
Jun 13, 2009
331
107
SoCal
PS: After the CPU upgrade I noticed that Mohave reports the RDIMMS as running at 1333MHz even though the original spec 85MP3S9M032K from OWC shows them as PC8500 1066 MHz RDIMMS. Is Mohave correct? If so why wouldn't OWC have mentioned that these were capable of higher speed with the X series CPUs? Strange.
 

tsialex

macrumors 603
Jun 13, 2016
5,298
6,019
Brazil
PS: After the CPU upgrade I noticed that Mohave reports the RDIMMS as running at 1333MHz even though the original spec 85MP3S9M032K from OWC shows them as PC8500 1066 MHz RDIMMS. Is Mohave correct? If so why wouldn't OWC have mentioned that these were capable of higher speed with the X series CPUs? Strange.
It's very common that faster memory are down clocked to fit specific computer needs. RAM foundries only made 1333MHz memory around 2010/2011. Most Mac Pros from factory had 1333MHz RAM even if the original processor only supports 1066MHz, after second half of 2010.
 

msh

macrumors 6502
Original poster
Jun 13, 2009
331
107
SoCal
It's very common that faster memory are down clocked to fit specific computer needs. RAM foundries only made 1333MHz memory around 2010/2011. Most Mac Pros from factory had 1333MHz RAM even if the original processor only supports 1066MHz, after second half of 2010.
Interesting. I knew that RAM chips can support multiple speeds but I thought it was only downward from their rated speed not upward. A pleasant surprise.
 

tsialex

macrumors 603
Jun 13, 2016
5,298
6,019
Brazil
Interesting. I knew that RAM chips can support multiple speeds but I thought it was only downward from their rated speed not upward. A pleasant surprise.
It's a 1333MHz DRAM that the SPD was programmed to have a 1066MHz config and was sold as 1066MHz. It's very common.