iMac repaste

[CooperBox]

I'm currently doing a complete refurbish of (yet) another iMac.

In the following photos one can see that previously someone was over-zealous in appying the thermal paste onto the cpu:



Below after cleaning.
Some of the excess paste had previously oozed it's way underneath the CPU thin (plastic?) protective coating.



Is this detrimental to CPU function? Particulary the small bead of paste on one capacitor (lower right).



During a refurbish I like to be meticulous and cut no corners, and if deemed necessary prefer to clean this 100% before repaste/heat-sink reinstall.

I have little doubt that the above 2 photos will excite the likes of LightBulbFun, who in this festive season, seeing several macro photos of a cpu may possibly get higher than eating a dozen mince pies heavily dowsed in Armagnac......(thoughts of yesterday lunchtime)........
So now a question if I may. MacTracker identifies the G4 cpu as a 7455 v3.3 in iMac6,1 thro iMac6,3 (these models being 1GHz and 1.25Ghz). Is there any differences in the cpu themselves, or is the increase in clock speed acquired from some wizardry on the logic board?

 

[AphoticD]

I'm currently doing a complete refurbish of (yet) another iMac.

In the following photos one can see that previously someone was over-zealous in appying the thermal paste onto the cpu:

View attachment 884812

Below after cleaning.
Some of the excess paste had previously oozed it's way underneath the CPU thin (plastic?) protective coating.

View attachment 884813

Is this detrimental to CPU function? Particulary the small bead of paste on one capacitor (lower right).

View attachment 884814

During a refurbish I like to be meticulous and cut no corners, and if deemed necessary prefer to clean this 100% before repaste/heat-sink reinstall.

I have little doubt that the above 2 photos will excite the likes of LightBulbFun, who in this festive season, seeing several macro photos of a cpu may possibly get higher than eating a dozen mince pies heavily dowsed in Armagnac......(thoughts of yesterday lunchtime)........
So now a question if I may. MacTracker identifies the G4 cpu as a 7455 v3.3 in iMac6,1 thro iMac6,3 (these models being 1GHz and 1.25Ghz). Is there any differences in the cpu themselves, or is the increase in clock speed acquired from some wizardry on the logic board?

The excess goop won't do any damage. You can easily peel off that thin gasket to clean underneath if you like. I have often thrown the gaskets away. In my opinion, they are only to reduce dust build up at the CPU and have zero benefit to heat dissipation. I haven't been able to scientifically prove the theory, but I imagine it would likely cool easier without the gasket as airflow could potentially hit the sides of the CPU die.

In most cases, Apple did install CPUs with ratings specific to the clock speed rating, That is a 1250MHz rated 7445, which means that if you wanted to try, you could easily crank it up to 1333MHz or possibly higher. The CPU speed is based on the bus speed multiplied by the PLL multiplier.

The PLL multiplier for 1.25GHz is set at 7.5 x 167Mhz (system front side bus). Take a look at this page for specifics of which resistors to jump to get a higher clock speed: https://www.ethernetworks.de/imac_g4_usb2_overclocking.html

If you have a 1.0GHz model (i.e 15-inch), it might be worth trying to bump up to 1.25GHz as this is just a change of four resistors: removing resistors at R378 and R379 and then jumping/closing R380 and R381 (directly to the right of the original two). I have had success using a tiny solder blob to bridge the resistors in other PowerPC Macs, but have never owned an iMac G4.

Merry Christmas

 

[CooperBox]

Thanks for your reply. Interesting comments about the wafer-thin 'gasket' that cover the cpu, as I've often wondered what real purpose it fulfilled.
I was just being inquisitive about the different clock speeds, but not for any practical purposes. However your comments and the supplied link explain it well. For info this iMac is my preferred 1.25GHz model and I'll leave the resistors well alone as shown below:



Currently awaiting receipt of an SSD to pop into this iMac. Was expected 2 days ago but think Santa took the wrong Amazon Greyhound sleigh......
Seasons Greetings from SW France! 🍷🥂🎅

 

[z970]

Yeah, that plastic layer is present in several Macs of the era. They're a major PITA to maneuver around while cleaning, so I usually opt for taking them off entirely. The CPUs always work without a hitch afterward.