Bad RAM on PowerMac G5 - Interpreting POST

Question

I have a problem with RAM DDR400 on a PowerMac G5 2x2 GHz (July 2004 model with 8 DIMM slots) equipped with 4 x 256 Mo and 2 x 512 Mo SDRAM all installed in pairs by the vendor .
Recently, after updating to OSX Tiger - 10.4.7 or 8 - I discover that the 4 x 256 Mo memory items are well recognized by OSX - according to "About this Mac" and "System Infos" - but not the 2 x 512 Mo SDRAM...!!! So, my G5 showed I only had 1 Go RAM instead of 2 Go. And I guess it used only 1 Go.
I tried everything from Tiger clean install to disk repair, PRAM reset, etc ... with no effect at all on the "missing" RAM's recognition by OSX.
Then I ran the "Apple Hardware Test" software (CD v.2.2.4). It shows - in red alert - the two 512 Mo DIMMs as "0-512 Mo" RAM (instead of 512 Mo fit) with one indicated as "failed POST". Then the quick test comments this failed DIMM5 (J42) with the following error message : "post/0/2048"...!!!
Did somebody knows what the Power-on Self Test (POST) "0/2048" error exactly means ??
Is there somewhere a kind of "list" referencing POST errors ?
Initially the 2 Go RAM were fully recognized by Panther 10.3.8 (cf. "System Infos") with the G5 firmware 5.1.8f2. However, when upgrading to Tiger (10.4.0), I also updated my G5 firmware with 5.1.8f7 (as recommended for June 2004 PowerMac G5).
Is it possible that the G5 firmware update "damaged" or "changed" something related to the RAM's access by OSX Tiger ?
Any help or suggestion will be welcomed. Thanks in advance.
Grisou403 - from Paris, France
PowerMac G5 2x2 GHz   Mac OS X (10.4.8)  

Answer 1

To maclover and DaddyPaycheck and all concerned readers
I successfully solved my problem of "disappeared" RAM memory (DDR400) on my PowerMac G5 2x2 GHz ( (July 2004 model with 8 DIMM slots). Mostly with help from two readers - namely MACLOVER and DADDYPAYCHECK who reacted quickly to my call for help, both with a very good advice. And I thank them for that. Because it's really helpful when you're faced with a serious problem never encountered before.
So, being now out of trouble I wrote this "debriefing" note to testify about the process of how to identify and solve the bug.
This could possibly help other "normal" Mac users... I mean non-expert like me.
1 - About the problem's "origin".
I discovered the "missing" RAM just by chance after looking at "About this Mac" and "System Infos" after updating my OSX Tiger system from 10.4.5 to 10.4.7 and 4.8. "About this Mac" mentioned only 1 Go of RAM (instead of 2 Go physically installed 2 years ago). The "System Infos - memory" panel" confirmed that only my four 256 Mo DIMMs were "recognized" and "active" (mentioning type, speed and "state" OK). My two 512 Mo RAM units have "disappeared" and the DIMM slots were identified as "empty"! This diagnosis has been confirmed by "Onyx" and Mac Pilot" utilities. So, it's trustable.
Then I ran the "Apple Hardware Test" software (CD v.2.2.4). The "Quick Test" immediately identified the problem. Its "Hardware Profile" panel showed the 4 x 256 Mo DIMMs as active with correct size/speed. But AHT displayed a "red alert" about the two 512 Mo DIMMs (seated into J41 and J42 slots) that were referred as "0-512 Mo" RAM (instead of straight 512 Mo) with one DIMM (J42) marked as "failed POST". The "Extended Test" provided additional data about the failing RAM with the error message (in red) : "post/0/2048/DIMM5/J42".
2 - No software nor system debugging
First, I suspected the OSX update to have changed something about the RAM's recognition by the System. So, I tried usual maintenance and correcting actions - repairing authorizations, restarting the Mac (even as single user), zapping the PRAM, etc. Then I reinstalled Tiger including a "clean install" from the Tiger DVD. Without any success... Because it has been later demonstrated that intrinsically this kind of "hardware bug" cannot be solved by software "manipulations"!
3 - Solution : Reinstalling the RAM
Thus I decided to turn to the RAM's direct check, as suggested by the two readers.
Initially, I was quite reluctant to put my hands on the memory hard because I never did it. But I found it rather easy to do. After reading the Apple knowledge base's memory replacement guideline ... and taking special care of static electricity (wearing a wire bracelet connected to the G5's case). This point is important as static electricity could definitely damage RAM memory cards.
So I removed the two 512 Mo DIMMs from their original slots and re-installed them into the adjacent pair of slots (in place of two 256 Mo DIMMs).
At the first restart under Tiger 10.4.8.. Bingo : "About this Mac" and "System Infos" panels displayed the expected "2 Go" of RAM. Both the RAM memory cards and the DIMMs slots are OK.
4 - The "Lessons" learned from this troubleshooting.
In conclusion, I would say that above-mentioned readers were right : in such case - "no show" RAM - the best option is to remove and inspect the DIMM and then - if cards and connectors looks good - to reinstall it correctly ... and carefully!
By the way, I would recommend to re-install the suspected DiMMs into a different pair of slots than the original ones. This "cross install" procedure allows to check the validity of both the RAM itself and the DIMM slots with only one manipulation. So there is no need to make another move for installing the RAM by size hierarchy. In my G5 bipro, RAM is now fitted (by pairs) in the DIMMs' rows 1 to 3 with a 256-512-256 Mo sequence and it works.
I would also strongly recommend to run the "Apple Hardware Test" (AHT) software to get a more detailed diagnosis. For example, AHT gave me the error message :"post/O/2048/DIMM5/J42".
While being unable to find a list of POST error codes, I can now try to "reasonably explain" this kind of error message I got. The "Power-on Self Test" (POST) item "0/2048" obviously refer to the RAM size : total "installed" RAM was 2048 Mo (2 Go). But the "0" prefix means that zero Mo were "recognized" (or "active") from some DIMM card(s). Then the "DIMM5/J42" item pointed out to the fifth DIMM (J42) that, in my case, was the "single failure point". But, of course, as RAM is working by pairs on the PowerMac G5 bipro. if just one DIMM "failed" the associated DIMM is also "neutralized" - even if it does not "failed".
Finally, this RAM trouble makes me more comfortable to do still "simple' - but sensitive - maintenance and repair inside my Mac... while being 65 with no special skill in computer's knowledge. So I would say everybody else can succeed too.
Again, many thanks to MacLover and DaddyPaycheck for quick help ...
and Christmas Greetings to all Apple Discussion readers.
Power Mac G5 biprocessors 2 x 2 GHz (July 2004)   Mac OS X (10.4.8)