Buying decision

[ehume]

There are a number of concerns raised in this thread which are worth discussing.

For starters, root-cause analysis on how your chip's IHS "got dented"? If you don't know how it happened the first time around, and don't develop protocols to prevent it from happening again, then this thread is going to become a bit of a "rinse and repeat" down the road once you bend the IHS on whatever replacement CPU you intend to purchase.

Second, you are concerned that a lapped CPU will result in cooling data that are invalid for comparison to non-lapped ("stock") IHS, but at the same time you acknowledge you are generating data with completely invalid (for the purpose of data comparisons) prototype HSF's?

You see what I'm getting at here? You have nothing in the way of ensuring you don't trash your next CPU's IHS, and you aren't generating apples-to-apples data anyways because you aren't being given retail HSF samples for your tests.

So...who cares if you lap your existing CPU IHS and just add one more disclaimer to the existing questionable cooling results?

You raise good points. I'll get to the denting process in a minute.

I know when the CPU was dented, and by which heatsink. That one is going back to the manufacturer tomorrow.

The denting occurred after the last test was run for that review. Thus, it was never used for comparisons in its damaged state. I cannot in good conscience ever use the old CPU again for testing heatsinks. That is why I bought a new one. I'm just lucky I tried this new orientation after the review was done.

You raise a good point about process. I want to avoid "rinse and repeat." I think I will look at the bottom of heatsinks -- the contact surface -- from here on in. The manufacturer tells me they put an 0.8 - 1mm convexity on their surfaces. It will be interesting to record the convexity -- as far as I can measure it -- on future heatsinks.

You are actually the right one to talk to about all of this. A correspondent in an SPCR thread said that CPU's tend to arrive with a little concavity in the IHS's. Have you found this to be true? I also read somewhere that a particular manufacturer puts an excessive convexity on their heatsinks, so that after you use one of theirs, the CPU tends not to work so well for subsequent heatsinks.

The denting process seems to be very interesting. I do not find the old 4790k to be visibly dented. Yet when I tested the old D15 on the old 4790k, the cores got hot rapidly -- just like my 4770k when it runs up against its thermal limit. That meant inferior TIM on the 4770k, just like the TIM on the Ivy Bridge you delidded. OTOH, when I tested the same old D15 on the new 4790k, the D15 cooled well again.

Here's a hypothesis: a CPU is concave when the IHS is stuck to the silicon by the sub-IHS TIM. My old 4790k is no longer good for CPU testing because the last heatsink did something to it to cause the IHS to get unstuck from the silicon. In essence, I have a damaged TIM there, if the hypothesis is correct. That would fit the visible evidence: no denting of the IHS. When you dissected your Ivy Bridge, you were able to deduce that there was a gap between the IHS and the silicon. If my hypothesis is correct, there is now such a gap on my old 4790k.

But how can I test the hypothesis? I can't look under the IHS. Knocking the IHS off would disrupt any underlying TIM, making it impossible to find out what it happening. I suppose I could test the CPU at lesser, perhaps much lesser Voltages to see if an ordinary heatsink can cool it at all.

In the mean time, I do have the new CPU, and it works better than the old one.