MP 1,1-5,1 (Solved! Thank you!!) Mac Pro 5,1 is cool with 4 RAM sticks, but won't turn on with 5, 6, 7, or 8

[centradragon]

Ey mates! I have a cool old 5,1 that I wanted to inject additional life into. Long story short, it currently has 32GB of 1066 MHz DDR3 (8GB each in 4 slots next to one processor), and I bought 32GB more RAM (same size and specs, different brand) to fill the remaining 4 slots with.

I've already tested all the RAM and they work great in any combination in the first four RAM slots — that being said, installing more RAM in ANY combination (just one stick, just two, four, one brand or another, etc) in the remaining four slots does one thing:

Computer won't turn on, and the white light by the button blinks endlessly.

If I remove the offending RAM from those slots, it boots up perfectly. I can't install just 4 sticks into those slots either; it just won't turn on.



I've searched EVERYWHERE and I can't figure out what I'm doing wrong. Is it possible I have a bad CPU tray? The RAM seems well-seated and I can't imagine I'd screw up one side and not the other, multiple times. It ain't my first rodeo, but I'm just baffled on this one.

Thanks for reading, and I hope ya'll are having a good week!

 

[tsialex]

Are you sure that your DIMM are all the same? Maybe you bought UDIMM instead of RDIMM or the inverse. You can't mix UDIMM with RDIMM.

Besides UDIMM vs RDIMM, maybe your second Xeon is defective, or your tray. To check if it's your Xeon, just invert the Xeons on the sockets, install the original Xeon A on socket B. If then the slots 5 to 8 work and 1 to 4 stop working, it's the Xeon and not the tray.

 

[centradragon]

Are you sure that your DIMM are all the same? Maybe you bought UDIMM instead of RDIMM or the inverse. You can't mix UDIMM with RDIMM.

Besides UDIMM vs RDIMM, maybe your second Xeon is defective, or your tray. To check if it's your Xeon, just invert the Xeons on the sockets, install the original Xeon A on socket B. If then the slots 5 to 8 work and 1 to 4 stop working, it's the Xeon and not the tray.

Mate, you're an absolute godsend!

Crucial CT102472BB133936FD1 8Gb 2RX4 PC3-10600R DIMM
OWC 8GB PC-8500 1066MHz DDR3 ECC SDRAM (OWC85MP3W8M32K)

I'm 99.9% sure I mixed registered and unregistered RAM, like you suggested. I can't believe it! I learned something new today and I'm so happy it's my own lack of knowledge and not my machine being broken.


Thank you so much, and I hope you have a wonderful day. Pretty sure this is case closed!

 

[tsialex]

Mate, you're an absolute godsend!

Crucial CT102472BB133936FD1 8Gb 2RX4 PC3-10600R DIMM
OWC 8GB PC-8500 1066MHz DDR3 ECC SDRAM (OWC85MP3W8M32K)

I'm 99.9% sure I mixed registered and unregistered RAM, like you suggested. I can't believe it! I learned something new today and I'm so happy it's my own lack of knowledge and not my machine being broken.


Thank you so much, and I hope you have a wonderful day. Pretty sure this is case closed!

A lot of OWC RAM is UDIMM. It's easy to see, the DIMM don't have the register controller on the PCB, at the centre.

Your OWC RAM are UDIMM, see here:

OWC 32GB DDR3 1066 MHz UDIMM Memory Kit (4 x 8GB, Mac)

Buy OWC 32GB DDR3 1066 MHz UDIMM Memory Kit (4 x 8GB, Mac) featuring 32GB (4 x 8GB) Capacity, 1066 MHz Clock Speed, PC-8500, 240-pin UDIMM, 1.5V, 7-7-7-20 Timings, ECC, Apple-Specified Thermal Sensor, Module Bandwidth: 8.5 GB/s, Compatible with the Select Mac Pros. Review OWC null

www.bhphotovideo.com

Without even searching, I know that your Crucial DIMMs are Registered, see the R at PC3-10600R.