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A fix of sorts for PowerBooks with lower RAM slot issues Laptop Macs
Many PowerBook G4 users are experiencing failures of the lower memory slot. I have found a workaround for the problem, though not quite a full solution (as it won't survive a reboot). Note that very little testing has been done on this fix, but I have used it on my PowerBook with 100% success.

First, I confirmed my lower slot is not fried by starting up with a single DIMM in the lower slot, which worked. However, the Mac still will not recognize the lower DIMM if there is memory in both the upper and lower slots. This may be different to what others are experiencing so your mileage may vary.

[robg adds: Note that this hint involves the use of Open Firmware, and you could permanently damage your machine by following this procedure. Proceed at your own risk, as macosxhints.com will not be held liable for any damages you cause to your own machine.

I was on the fence on running this hint, but when I ran the Google search linked above, it seems this is a somewhat widespread issue...and maybe this will help someone get back some currently unusable RAM. Just keep in mind you could also really damage your Mac when working in Open Firmware.

Read on for this user's workaround to the memory slot recognition issue...]

As I said, my PowerBook was physically detecting the RAM in Open Firmware, but simply not mapping it to any address space. Logic dictates that if the RAM isn't properly mapped to an address, it will not be visible in OS X. Thus the possibility exists to increase the size of your system RAM in Open Firmware by changing these mappings.
  1. First of all a note about RAM module sizes. Sizes appear to be in hex:
    • 10000000 = 256mb
    • 20000000 = 512mb
    • 40000000 = 1gb
    • ... and so forth ...
    You need to use the sizes above to map your RAM to relavent address space.
  2. Reboot into Open Firmware. Do this by holding Command-Option-O-F just after the system chimes during the boot process.
  3. tThis will bring you to the white Open Firmware prompt, 0>. From here, you need to navigate to the memory device tree by typing dev /memory.
  4. To display the details about the current memory mappings, type .properties.
  5. Here's how I mapped my PowerBook's memory modules to address space -- remember that everything left of the ">" is the prompt:
    0> 0 encode-int 10000000 encode-int encode+
    2> 10000000 encode-int 40000000 encode-int encode+
    4> encode+
    2> " reg" delete-property
    2> " reg" property
    0> mac-boot
    Here's how those commands work. The first line loads the location of my first memory module onto the Open Firmware stack. In this case, it starts at address space 0 and is 10000000 (256mb) in size. The next line loads my second memory module onto the stack, starting at address 10000000 (directly after the first module), and it's 40000000 (1gb) in size. The third line encodes the two lines above together on the stack. The fourth line deletes the current address space mappings (the contents of the " reg" property). The fifth line pops my new memory mappings off the stack and onto the " reg" property. Finally, the last line starts the boot process for my Mac. After it boots, check System Profiler, and both DIMMs should be registering now.
There are two problems I can see with the use of this method. First of all, it is not persistent -- when you reboot your machine, these mappings will be lost and you will be back to square one. Second, and this is the biggie, why is Open Firmware not doing its job and mapping both modules properly in the first place? Is there a problem with it gauging the size of the memory in the lower slot when two modules are installed (i.e. faulty module)? Or is this just a firmware bug? Anybody have any answers ... anybody at all?
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A fix of sorts for PowerBooks with lower RAM slot issues | 13 comments | Create New Account
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A fix of sorts for PowerBooks with lower RAM slot issues
Authored by: k0t1k968 on Mar 04, '08 08:38:58AM

This hint worked for me. Now if some of "Open Firmware" experts can tell us how to make this change permanent so it survive reboot.

---
Andrei Tchijov
Leaping Bytes, LLC



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A fix of sorts for PowerBooks with lower RAM slot issues
Authored by: 1amzave on Mar 04, '08 03:21:44PM

Note: I am *far* from Open Firmware expert, so this may well be completely useless, and I *certainly* wouldn't recommend messing with this without a great deal more prior research, but:

From what I (think I) know, if this were to be made persistent, it would likely be done via nvram (non-volatile ram). You can check nvram variables via `nvram -p` - on my system, this lists a variable "ram-size" as a hex number tht reflects the amount of memory I have installed (0x40000000, or one GiB). I *highly* doubt just changing this to whatever your ram size should be would do it, but it seems like it might potentially be involved.

(Also note - I don't have this particular problem, so my system may be different than that of people who do have the problem.)



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A fix of sorts for PowerBooks with lower RAM slot issues
Authored by: jolomo on Mar 06, '08 11:07:25AM

I've got a PowerBook G4 with two 1GB DIMMs. Was this the right syntax to use?

0> dev /memory
0> 0 encode-int 40000000 encode-int encode+
2> 40000000 encode-int 40000000 encode-int encode+
4> encode+
2> " reg" delete-property
2> " reg" property
0> mac-boot

That got me booted with both recognized, but when memory usage got to about half (according to Activity Monitor) the system completely froze. Thanks



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A fix of sorts for PowerBooks with lower RAM slot issues
Authored by: ash7 on Mar 04, '08 08:41:06AM

Not so sure this is going to work out... I've been able to trick my mac into re-recognizing the slot (not using this trick), only to be greeted with a frozen laptop a couple days later.

I'll try it out and see if I get the same results.



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A fix of sorts for PowerBooks with lower RAM slot issues
Authored by: robogobo on Mar 04, '08 05:47:28PM

I have a better solution.

1. Get a good insurance policy, one that covers any accidental loss.
2. Backup.
3. "Fix" your Powerbook:
a. open window, insert PB, release. Or
b. drive to wal-mart, roll down window, leave PB on seat, go shopping. Or
c. run a bath, soak PB, repeat.
4. File a claim. Get new computer.



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A fix of sorts for PowerBooks with lower RAM slot issues
Authored by: ngaubert on Mar 05, '08 10:10:24AM
If you want to store your fix so that it survive to reboot, you can store it in the nvramrc which is an NVRAM location reserved for user-defined commands used during system initialization.
nvedit let you edit the nvramrc, then you type the command you want to run at each boot time (that would be your script except the reboot part otherwise you would find yourself in a constant reboot loop ;)
then you add unselect
then type ctrl+c to exit the editor
then nvstore will store your code into the nvramrc, then you should tell your computer to run the command you have typed at each boot time by telling it to use the nvramrc (setenv use-nvramrc? true) then the reset-all command will reboot your mac.. so that's what you should type in the open firmware prompt :

nvedit

0 encode-int 10000000 encode-int encode+
10000000 encode-int 40000000 encode-int encode+
encode+
" reg" delete-property
" reg" property

unselect

<ctrl-c>

nvstore

setenv use-nvramrc? true

reset-all


In case you want to return to your original configuration all you have to do is reset your nvram. This is usually done by pressing the Command-Option-P-R keys while you turn on your computer until the start sound chimes again.
I haven't try your script because I don't have a powerbook, but I did used the same technique to enable the extended desktop on my old ibook see : [link:http://www.rutemoeller.com/mp/ibook/ibook_e.html] for reference.

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A fix of sorts for PowerBooks with lower RAM slot issues
Authored by: swampg8rs on Mar 05, '08 06:57:03PM

the original hint works great. gives me back my lower slot. however, doing the nvedit stuff isn't working. i'm pretty sure i'm entering everything as written, but when it reboots, no lower slot again. has anyone else gotten this to work?



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Apple seems to be aware
Authored by: punka on Mar 05, '08 09:37:55PM
Just FYI, Apple began to extend in-warranty repair for the faulty RAM slot [apple.com] in June of 2007. Only continued feedback from those affected can increase the scope of the repair extension program.

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it doesn't work
Authored by: kanny on Mar 08, '08 05:30:03AM

It kind of fools the system to believe as if it has got 1GB (two 512MB). But when the system memory exceeds 512MB and tries to write to the otherwise non-functional lower module, the system freezes - because it can't.

I followed the procedure and boot with sys-profiler showing 1GB memory. However it showed type and speed as "unknown" for the lower slot. So, my question is are you able to really use the increased capacity ?

And btw, good that this procedure doesn't last a reboot.



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A fix of sorts for PowerBooks with lower RAM slot issues
Authored by: k0t1k968 on Mar 08, '08 04:57:39PM

Unfortunately trick with nvedit/use-nvramrc? does not work. To the best of my understanding how boot process works, the reason is that nvramrc script gets executed before step on which memory gets "discovered". I do believe that it is possible to avoid it (by explicitly invoking that hardware-testing step from nvramrc script), but could not figure out how to do it :(.

Obviously some % of "broken" PB will become even more "broken" after this fix. If you really have fried memory slot and/or fried memory, fulling with firmware will not make it work. But it does work wonderfully on my wife's PB. She really can feel the difference when playing WoW, so it is quite obvious that PB is able to use memory in that slot.

---
Andrei Tchijov
Leaping Bytes, LLC



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A fix of sorts for PowerBooks with lower RAM slot issues
Authored by: logged on Mar 10, '08 10:15:35AM

hi all, another trick worked for me to make the lower ram recognized by my pb either if sometimes at reboot you've to follow once again this procedure:
simply invert the sodimm ram! (put the lower on the upper etc.).
By the way this demonstrate that the ram slot and the sodimm ram aren't totally fried. The problem is that when the system allocates more memory into an application -i assume more than a half of the total ram, the system collapses into a kernel panic. And i believe that same will happen either using the hint described above. Since now, by myself, i've changed the hard disk, used techtool pro, diskwarrior, i've dis-allowed nap using a developer application, with no results.. I hope to ear news from you, as apple rests in peace...
adelchi, rome, italy



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A fix of sorts for PowerBooks with lower RAM slot issues
Authored by: carterj on Mar 13, '08 01:38:03PM

Hm, interesting approach.
Sadly, it does not work on my PB 15". The System Profiler shows 2 GB, but after some time the PB freezes. For example, launching memtest causes the pb to freeze every time when memtest attemps to lock the memory (thus accessing the RAM "forced" via OpenFirmware).

It's clear that there is a hardware failure in the lower memory slot that cannot resolved via software hacks. Apple should do the right thing and 1) extend the serial number range of PBs qualified for the repair program and 2) extend the duration of the program to 3 to 5 years after the purchase of the powerbook (currently you cannot possibly use the program, since the last powerbooks were sold more than 2 years ago, and the program is only valid for 2 years after the purchase of a PB)



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A fix of sorts for PowerBooks with lower RAM slot issues
Authored by: swampg8rs on Mar 14, '08 07:22:53AM

after further use, mine locks up too after a while :-(



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