15" PowerBook G4, replacing logic board: thermal paste on CPU?

[J.Appleseed]

Hey all,

I currently have a PowerBook G4, which most likely has a dead graphics chip, and I would like to replace its logic board with one that has been stripped from a working unit.

However, if I follow this iFixit tutorial, at step 21 it states that I should reapply the thermal paste that is situated between the CPU and the heat sink.

This means that I should use the thermal paste as some sort of airtight seal between those two parts, am I right? I shouldn't have to remove the CPU from the logic board (which would be impossible on a laptop anyways).

I'm sorry if this is a bit of a 'dumb' question; it's just that I never really modified anything on my computers other than the harddrive and RAM. This is my first time swapping logic boards and I really wouldn't want to screw up a perfectly fine one

 

[eyoungren]

I've replace a few logic boards. Never redid thermal paste. One of them was the 12" PowerBook (my wife's PowerBook) and it mentioned that. But as I didn't have any and had never planned to do it - I didn't. Hasn't been a problem, her Mac is still running fine.

They probably mean thermal paste between the heat sink and the cpu.

 

[J.Appleseed]

I've replace a few logic boards. Never redid thermal paste. One of them was the 12" PowerBook (my wife's PowerBook) and it mentioned that. But as I didn't have any and had never planned to do it - I didn't. Hasn't been a problem, her Mac is still running fine.

They probably mean thermal paste between the heat sink and the cpu.

Thank you so much for your quick reply. I actually bought the thermal paste iFixit recommends this afternoon, so I was most definitely planning on following their exact instructions.

I just didn't know if I understood the whole process correctly, and turns out I didn't really think it through.
Furtunately, I did now so I'll at least have somewhat of a clue what I'm doing

 

[mizaco]

How valuable do you think those Power books are compared to Intel based units?

 

[eyoungren]

How valuable do you think those Power books are compared to Intel based units?

In sentimental or personal value? Or in monetary value.

If the latter, not much. Which means…you're missing the point.

 

[J.Appleseed]

In sentimental or personal value? Or in monetary value.

If the latter, not much. Which means…you're missing the point.

Well, in the Netherlands I see them being sold for 200 euros, minimum. I'd say that's pretty expensive for a 10 year old computer

But you're right - I'm not doing this for resale value, I just think it'd be a shame to just throw this fine computer away and it's always nice to have a second laptop! Also, it's a nice and interesting project for me.

 

[eyoungren]

Well, in the Netherlands I see them being sold for 200 euros, minimum. I'd say that's pretty expensive for a 10 year old computer

But you're right - I'm not doing this for resale value, I just think it'd be a shame to just throw this fine computer away and it's always nice to have a second laptop! Also, it's a nice and interesting project for me.

Exactly!

And that's what I was trying to point out to the other poster. We all have our various reasons for using PowerPC Macs, but if it was based solely on money a lot of us would not be in this particular forum.

 

[mayuka]

However, if I follow this iFixit tutorial, at step 21 it states that I should reapply the thermal paste that is situated between the CPU and the heat sink.

At some point in time Apple was supposedly applying too less thermal paste. At least, that's what was being told in some forums at that time. Often it was reasoned that the thermal paste could dissolve and that the processors will overheat in the distant future. What should I say. I'm using my Powerbook G4 1,5 GHz since a couple of years, often running at full speed. Never had any trouble with it. I guess, that's just one of those forum myths that's talking on the iFixit site. It's not the amount of thermal paste, but more the way you apply it. Unless the processor or the fan(s) are not acting oddly, I would not worry. Just inspect the logic board closely before using it. There are more ways you could go wrong while re-applying thermal paste, instead of just using the logic board.

 

[J.Appleseed]

At some point in time Apple was supposedly applying too less thermal paste. At least, that's what was being told in some forums at that time. Often it was reasoned that the thermal paste could dissolve and that the processors will overheat in the distant future. What should I say. I'm using my Powerbook G4 1,5 GHz since a couple of years, often running at full speed. Never had any trouble with it. I guess, that's just one of those forum myths that's talking on the iFixit site. It's not the amount of thermal paste, but more the way you apply it. Unless the processor or the fan(s) are not acting oddly, I would not worry. Just inspect the logic board closely before using it. There are more ways you could go wrong while re-applying thermal paste, instead of just using the logic board.

Hmm, alright then. I suppose the unit would turn itself off automatically if it would get too hot anyway, wouldn't it?

I have indeed read that there are several ways to apply thermal paste (a line, several lines, just a drop and let it spread automatically, ...) and it seems to vary even within certain processor types, so I guess I'll just set the logic board in first and then see how it goes.

If I have any luck I will even try and do it today, but I'll definitely keep you guys updated!
Thank you so much for your kind advice.

 

[eyoungren]

Hmm, alright then. I suppose the unit would turn itself off automatically if it would get too hot anyway, wouldn't it?

Yes! It's called thermal shutdown and my wife's PowerBook experienced it several times when I replaced her screen.

I had to take the logicboard out to do that which meant removing the heat sink. I stupidly assumed that the heat sink wasn't needed so put the thing back together without it. It ran for about three minutes or so and then bam! Instant shutdown.

It's a protective measure that's hardcoded. It shuts it down at a temperature that is still safe to the logicboard but beyond normal operating temperature.

Needless to say, I put the heat sink back in to my wife's Mac and after a replacing a few other parts I broke because the tolerances inside the 12" PB are so tight her PowerBook has run fine ever since.

 

[mayuka]

Hmm, alright then. I suppose the unit would turn itself off automatically if it would get too hot anyway, wouldn't it?

Yes. They included the feature since they introduced the G4 mobile processor I think.

Applying thermal paste is biased. Everyone does it differently. You won't get any recommendation from me in this regard, except that avoiding it is sometimes the best solution. If you accidently remove the heat sink, that's another thing of course.

 

[J.Appleseed]

Yes! It's called thermal shutdown and my wife's PowerBook experienced it several times when I replaced her screen.

I had to take the logicboard out to do that which meant removing the heat sink. I stupidly assumed that the heat sink wasn't needed so put the thing back together without it. It ran for about three minutes or so and then bam! Instant shutdown.

It's a protective measure that's hardcoded. It shuts it down at a temperature that is still safe to the logicboard but beyond normal operating temperature.

Needless to say, I put the heat sink back in to my wife's Mac and after a replacing a few other parts I broke because the tolerances inside the 12" PB are so tight her PowerBook has run fine ever since.

Yes. They included the feature since they introduced the G4 mobile processor I think.

Applying thermal paste is biased. Everyone does it differently. You won't get any recommendation from me in this regard, except that avoiding it is sometimes the best solution. If you accidently remove the heat sink, that's another thing of course.

Update time!

So I took apart the Mac, and when it came to replacing the logic board I decided to apply the thermal paste anyway. I was very nervous when I booted it up again but it's alive!

It's running great. I'm going to install Leopard tomorrow (I figured I could share my MacBook Pro's optical drive but turns out I can't install an OS through that), and I'll go and look for a new battery and 2GB of RAM so that it'll run smoothly.

I'm so glad I got this beauty working again Thank you so much for all the help!

Old logic board out, new one in!

Next to my MBP, with the Leopard install disk being shared.

 

[eyoungren]

Update time!

So I took apart the Mac, and when it came to replacing the logic board I decided to apply the thermal paste anyway. I was very nervous when I booted it up again but it's alive!

It's running great. I'm going to install Leopard tomorrow (I figured I could share my MacBook Pro's optical drive but turns out I can't install an OS through that), and I'll go and look for a new battery and 2GB of RAM so that it'll run smoothly.

I'm so glad I got this beauty working again Thank you so much for all the help!

Old logic board out, new one in!
Image

Next to my MBP, with the Leopard install disk being shared.
Image

Nice to see! Another PowerBook saved!

Enjoy your Mac!

 

[mayuka]

congrats! great work!