External Cache Failure & kernel panics

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JAJ - 12 Dec 2007 18:24 GMT

Hi all, am neither an expert especially with OSX but could do with some
advice ..

Using a Quicksilver G4 Dual 1GHz running 10.4.11.
System Profiler tells me:

Power On Self-Test:

Last Run: 12/12/2007 5:11 pm
Result: Failed
Failure type: External cache

and since recently, have kernel panics constantly on bootup. It is getting
tricky to boot from CD's or External HD, havn't tried another machine in
Target Mode yet but feel that something serious is up :(

Can just about boot (2nd or 3rd time) in Safe Mode and have done fsck -yf in
Single User Mode. Occasionally (!), The system appears as it should in OSX
but this is increasingly rare.

Can detail other semi-successful workarounds but will keep this short for now.

It sounds like a new logic board is on the cards (pardon the pun) ... any
thoughts on whether this is definitely the case and where to get one?

Am very fond of this old workhorse and won't upgrade for a while so it'll
need to be 'make do and mend' for now ..

Thanks,

J

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David Empson - 12 Dec 2007 23:14 GMT

(Note: this isn't about portable Macs, so I've added
comp.sys.mac.hardware.misc to the list of newsgroups and set followups
there.)

> Hi all, am neither an expert especially with OSX but could do with some
> advice ..
[quoted text clipped - 7 lines]
> Result: Failed
> Failure type: External cache

Ouch. That's a pretty serious hardware fault.

The "external cache" referred to is probably the level 3 cache between
the CPU and memory. If this is failing, you will have an extremely
unreliable computer, with crashes and data corruption.

Depending on the exact problem, it will basically mean the CPU is
sometimes reading junk out of memory instead of what is actually there.
As the fault is intermittent it may be heat related - you may find that
the computer starts crashing or corrupting data when it is trying to
work hard, or on particularly warm days (or it might only happen when it
is cold). It could also be localised to one particular part of the
cache, so it might only happen when that part of the cache is occupied.

Stop using the computer immediately, until the problem can be fixed.

> and since recently, have kernel panics constantly on bootup. It is getting
> tricky to boot from CD's or External HD, havn't tried another machine in
[quoted text clipped - 3 lines]
> Single User Mode. Occasionally (!), The system appears as it should in OSX
> but this is increasingly rare.

It is not a problem with the hard drive or file system, but continuing
to use the computer could _cause_ problems with the file system, because
you are likely to have corrupted data being written back to the drive.
The file system data structures and contents of your files are at risk.

> Can detail other semi-successful workarounds but will keep this short for now.
>
> It sounds like a new logic board is on the cards (pardon the pun) ... any
> thoughts on whether this is definitely the case and where to get one?

The Level 3 cache is on the processor card, not the logic board. The
self-test might be fooled into thinking the fault is in the L3 cache
when it is actually on the logic board, but I doubt it.

Replacing the processor card with a third-party processor upgrade may be
your best option.

It might be feasible to modify the system in some way so that it
disables the L3 cache at startup. If so, your computer may then work
reliably but it will be a lot slower.

Signature

David Empson
dempson@actrix.gen.nz

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JAJ - 13 Dec 2007 07:31 GMT

Thanks David,

Thought it was serious. I unplugged everything last night and am fortunate
to have been able to replace the desktop with a Powerbook which is how I can
still work. Lucky that I also had a chance to do most recent backups before
meltdown.

The heat issue does seem pertinent and I also recently installed the new
aluminium mac kybd which conflicted with my Asante 7 port USB hub causing the
mac to restart automatically on shutdown. Hence I had a lot of power up-
power down-power up instances until the conflict was identified and corrected
(by plugging the hub into a different USB port!)

So the old box has been working rather hard of late.

I will have a look at the other newsgroup and keep an eye on that.

Thanks again,

James

>(Note: this isn't about portable Macs, so I've added
>comp.sys.mac.hardware.misc to the list of newsgroups and set followups
[quoted text clipped - 48 lines]
>disables the L3 cache at startup. If so, your computer may then work
>reliably but it will be a lot slower.

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JAJ - 13 Dec 2007 16:49 GMT

Hi again,

Sorry to bother you, am being very thick but how do I access the newsgroup:

comp.sys.mac.hardware.misc ?

Thought it would be within macKB but cant find it. Suspect I'm being very
daft.

Thanks,

James

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David Empson - 13 Dec 2007 20:02 GMT

> Hi again,
>
[quoted text clipped - 4 lines]
> Thought it would be within macKB but cant find it. Suspect I'm being very
> daft.

Possibly not - if your news server doesn't carry it then you might have
trouble reading it. Your news client should be able to get a list of all
newsgroups hosted by your news server and find it within that (along
with a bunch of other Mac groups in the comp.sys.mac hierarchy).

These are the main ones I read. There are a few others but they aren't
as active or are for specialised areas such as programming.

comp.sys.mac.apps
comp.sys.mac.hardware.misc
comp.sys.mac.hardware.storage
comp.sys.mac.misc
comp.sys.mac.portables
comp.sys.mac.system

If your full list of newsgroups is missing any of the above, then your
news server is missing some "core" newsgroups. You should contact them
and ask them to add the missing groups. They might have trouble getting
any articles in them, if they aren't carried by any news servers with
which they exchange articles.

If you have no luck, you might need to switch to a different news server
which is better connected or has better customer service. There are
commercial news providers such as supernews.com and giganews.com.

If all else fails, you can read for free at http://groups.google.com.

So far, I haven't seen any followups to the original message which I
cross-posted there, so you aren't missing anything as far as this thread
is concerned.

Signature

David Empson
dempson@actrix.gen.nz

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Mac Forum / General / Portable Macs / December 2007

External Cache Failure & kernel panics