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Heat problems on PowerBook G3 Bronze (Lombard)

Posted on 2004-08-31
Medium Priority
Last Modified: 2013-12-27
I have recently done a second memory upgrade on this Lombard and put in a new HD.  Now, with either the new or the old memory and HD, I get apparently random freezes, crashes, etc.  The machine seems to work normally when starting from cold but after a while (I assume when it starts to heat up) the freezes start.

The advice I have been given from several sources (but not here!) was to make certain that the processor board was properly seated on the mother board.  I have done this a number of times with no improvement.

I notice that the contact between the processor and the heat sink is mediated by a white compound which may have lost its effectiveness thanks to the heat sink having been pulled off a number of times.  It is normally recommended to replace such thermal compounds every time you reinstall the heatsink but the Apple Service Documentation makes no mention of this.

So - my questions :is this a known issue, do the symptoms accord with this being the problem, is it a good idea to replace this compound, if so what is it and where can I get some (I'm in Europe)?

I know that thermal compounds are available but reading an AMD report suggests that there are a number of different sorts and, rather than try and second guess the Apple designers, I'd rather get the "right stuff".  Or perhaps, given that the machine is now 4-5 years old, maybe better stuff?

Question by:Keith_Parr
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LVL 30

Expert Comment

ID: 11948668
You dont need to use the same stuff Apple did. Just get ANY thermal paste. It's cheap and might fix the problem. Use whatever you can find. Any decent PC supply store should have some.

Author Comment

ID: 11949245
Thank you Weed.  Is your suggestion based on experience with Lombards or general experience in the computer world?

If you read:

You will see why I am just a bit cautious and would prefer to go the Apple route if possible, after all they designed the thing and it worked so I have to assume they knew what they were doing <grin>.

While I agree that I may eventually have to accept the route you propose, once I remove the stuff that is there now (and remember I am only supposing that this is the problem, it could be something else and the white stuff is still working fine!) there will be no way to put it back and if it's special in any way then I will have a problem!

The point of the original question was to fiind out what should be there and to see whether we can find a source of it.
LVL 30

Expert Comment

ID: 11949375
The thermal paste is just plain old thermal paste. I added a big wad of it to my old lombard years ago. Removing what is there wont hurt it. And yes, it could be another problem entirely, but thermal paste is an easy thing to check.
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Author Comment

ID: 11951974
In fact you need a really big wad of it, when you remove the original pad there is a gap of more than 1mm between the processor casing and the heat sink.  So you really need a pad and not thermal grease. So now I am back hunting for the "right stuff" or I have to make a metal shim to fill that gap.  The advantage of the second choice will probably be that the result will be better than the original, but making a flat shim to the correct thickness is going to be a real PITA!

Looking at the surfaces involved this is clearly not the high tech mirror finish which is common with high performance processors these days.  Even so, I now have to fill that gap and a larger lump of goo will simply not cut it.
LVL 30

Expert Comment

ID: 11953489
Yes, a larger lump will be fine. The stuff dries pretty hard. Clearly the old lump filled the gap.

Author Comment

ID: 11961254
This goes against every other piece of advice I have seen about therrmal grease, including the recommendations from Arctic Silver which I believe to be one of the top brands.

The goal with thermal grease is to get the layer as thin as possible, between two touching surfaces, not to fill in the gap between the heat source and sink.

Further, the best thermal grease does not dry out, it is designed not to.  Again, look at the Arctic Silver web site.

So - to repeat my questions :is this a known issue, do the symptoms accord with this being the problem, is it a good idea to replace this compound, if so what is it and where can I get some (I'm in Europe)?
LVL 30

Expert Comment

ID: 11965320
You dont want to use grease, you want to use paste. And filling the gap is better than sticking some metal shim in there.

Any PC supply store will have some. And yes, replace the paste.

Expert Comment

ID: 12026371
First, avoid using thermal paste or grease to fill large gaps, it's all too easy to have excess grease flow off the edges of the chip onto chip or PCB traces and short circuit things. Remember that thermal paste not only conducts heat, containing metal, it also conducts electricity. Instead, use thermal pads to fill larger gaps. I bought a small pack at CompUSA for a few bucks, but the stuff is widely available from most any PC parts seller.

Secondly, your lockup symptoms are consistant with a failing L2 cache, a widely known Lombard issue.

Try a new processor daughtercard if available. If not, try using an L2 cache control (eg: PowerLogix's G3/G4 Cache Profiler) to turn the L2 cache off and see if that cures the crashes. If it does, the only real cure is a new daughtercard.


dan k

Author Comment

ID: 12061771
thank you macdan, this is really helpful, this is the first I have heard of a failing L2 cache being either a possible culprit or a well known Lombard issue.

I am "away from my desk" at the moment but I will be back in about a week.  I will then try the cache profiler as you suggest.

Menwhile, if you have any pointers to eg Apple documentation on the problem I would appreciate it.




Expert Comment

ID: 12086102
A hard drive that chronically overheats could also be the source of your problems.
When the freeze begins feel around the laptop for hotspots.

Author Comment

ID: 12088336
Thanks for the HD suggestion but I am pretty sure that's not it.  The hot spot is the processor.  I have experienced the same problems with two different HDs.

Expert Comment

ID: 12257148

I just want to shared my experience that the best way to use thermal paste is to paste it as thin as possible.  If you buy a good thermal paste, it will came with a credit-card look alike plastic.  It will also come with some template, usually some sticker template for Intel Processor.

You stick this template onto the heatsink, apply thermal paste onto the heat sink, and using the credit-card to spread it evenly, as thin as possible.  In the end, you have a thin layer of white thermal paste.  Pull out the template sticker, stick the heat sink on the top of the processor and lock it.

Make sure that you have to clean both processor and heatsink from the old thermal paste.

I used to believe that the more is the better.  But that's not the case.  I based my experience on Celleron, Pentium III, Duron, and Athlon processor.

Good luck.

Author Comment

ID: 12257674
Thank you idarmadi, you have confirmed what I have read about thermal grease on the manufacturers' web sites.

What I ended up doing was getting a small piece of aluminium sheet about the size of the processor top and approximately the right thickness to fill the gap.  I then carefully cleaned the heatsink, the piece of aluminium, and the processor, made a buttered sandwich of the piece of aluminium (a thin layer of thermal grease being the butter) and reassembled.

There is some good news and some bad news:

The good news is that the thermal solution works extremely well, the heatsink gets hotter than it ever did before.

The bad news is that it has not cured the problem so I have to investigate the L2 cache problem mentioned by macdan.


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