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tevion5

macrumors 68000
Original poster
Jul 12, 2011
1,880
1,375
Ireland
Earlier this week I booted up my G5 Quad to find only 12 of my 16GB Memory was showing up. I've had 16GB working without issue for 1-2 years now. DIMMs 4 & 5 were showing up empty despite that not being true. Haven't had to go fiddling inside for a long time so I'm surprised anything changed.

Today I decided to fix it so I shut down and reseated every DIMM for good measure. But when I booted up afterward I noticed only 4GB total was showing up! Now only DIMMs 2 & 3 appear in system profiler with all others marked empty. Hoping there isn't damage to the DIMM slots...

Is there something I'm doing wrong here?
Do I need to fire up open firmware and do a reset?
 

ziggy29

macrumors 6502
Oct 29, 2014
445
260
Oregon North Coast
I'd make sure the RAM slots are not broken, maybe use some compressed air into the slots in case there is some junk compromising the contacts. I also have a Quad with 8x2 GB RAM, and it has happened to me on occasion, too. But pulling out and reseating the RAM has generally worked for me.
 
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tevion5

macrumors 68000
Original poster
Jul 12, 2011
1,880
1,375
Ireland
I'd make sure the RAM slots are not broken, maybe use some compressed air into the slots in case there is some junk compromising the contacts. I also have a Quad with 8x2 GB RAM, and it has happened to me on occasion, too. But pulling out and reseating the RAM has generally worked for me.

Good idea, I'll try compressed air and see if that make's a difference.
 

AphoticD

macrumors 68020
Feb 17, 2017
2,081
2,877
Australia
I’ve had the same problem with my Dual Core G5. It ran fine maxed out for nearly 3 years and recently started only seeing 12GB of the 16GB installed.

Swapping modules and reseating appears to resolve it for a little bit and then the issue re-appears.

What I found is that when the 16GB is recognized, the system will operate ok for a little while and then intermittently lock up and the fans go into take off mode. I then reboot and the system will show 12GB total RAM and remain stable.

I feel that it’s the memory banks failing as this machine moves closer to its 15th year of operation.
 
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LightBulbFun

macrumors 68020
Nov 17, 2013
2,499
2,590
London UK
id reseat the RAM modules etc

and also if you can try some other RAM in the suspect slots

this will rule out of if its failing RAM or not

also don't forget about the "Diagnostic" tab in System profiler, this will tell you if the machine is Failing POST and disabling the RAM sticks, rather than them just not being detected
(and theres also Apple service diagnostic :) )

if your RAM sticks keep vanishing regardless of what you do, and especially if it shows up as a POST failure

then I fear its your memory controller that's failing, either BGA or die bump issues, where slowly RAM slots are physically being disconnected

this was a good symptom of the failing U3 North bridge on an AGP G5, however I think this is the first time I have heard of it happening on a PCIe G5
 

tevion5

macrumors 68000
Original poster
Jul 12, 2011
1,880
1,375
Ireland
this was a good symptom of the failing U3 North bridge on an AGP G5, however I think this is the first time I have heard of it happening on a PCIe G5

Lets hope it's not that bad! Been busy but I'll ticker with it tonight and go pair by pair. Forgot about the "Diagnostic" tab in System profiler. I don't think it was chiming on my last 2-3 boots either.
[automerge]1571744642[/automerge]
 
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tevion5

macrumors 68000
Original poster
Jul 12, 2011
1,880
1,375
Ireland
also don't forget about the "Diagnostic" tab in System profiler, this will tell you if the machine is Failing POST and disabling the RAM sticks, rather than them just not being detected

ahhh...

123.png

[automerge]1571782972[/automerge]

Cleaned the slots and a few of the other internals with compressed air.

I'm going pair by pair now to find a culprit and all seems okay after the first pair, will keep going...

222.png
 
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tevion5

macrumors 68000
Original poster
Jul 12, 2011
1,880
1,375
Ireland
Well! Went pair by pair and had no issues until the 3rd. Used the other pair I had left in 3rd slots and that worked. So at least slots of the first three pairs seemed to be okay and 75% of my DIMMs. One of the faulty pair DIMMs has a very mild looking scratch on the contacts on the back. Doesn't look toooo bad but it's suspicious.

I tried the faulty pair again in the 4th pair slots but no joy. Then as a last effort I swapped them top to bottom and for some reason it worked! All 16GB back in action, for now at least.

444.png
333.png

[automerge]1571785691[/automerge]
The beast is back in action
B52ECC8E-6694-46D8-ACD2-ED905B5F98D3.jpeg
 
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havokalien

macrumors 6502a
Apr 27, 2006
649
51
Kelso, Wa
Just FYI G5 ram slot solder issues on the G5. That huge board flexes with heat and cooling and starts getting cracked. Pushing and pulling ram into them after this much use and you may lose the slots altogether. Seen a bunch like this, The 8 ram slot versions are the worst.
 

havokalien

macrumors 6502a
Apr 27, 2006
649
51
Kelso, Wa
Lol I meant for the vanishing ram issue. SO many slots put more pressure/flex on the ram slots. The G5 is a solid machine, its really the whole "lead is bad" remove it from everything that causes the issue. Thats why everything built before the 80's like lasts forever and everything after seems to have a shelf life.
 
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