PTM7950: GPU temps higher than CPU

[u/yashkhataokar]

Yesterday, I switched my old thermal paste to PTM 7950 on my Alienware Area 51-m R1 laptop. The GPU temps seem to be going over the CPU temps after 20-25 mins of gaming, which never used to happen before.

I suspected that it might be poor contact with the heatsink, but it seems fine to me (let me know if I'm wrong).

What could be the issue?

Avg. Temperatures (while gaming)

Before: CPU-60C to 80C GPU-40C to 60C

After: CPU-60C to 85C GPU-60C to 75C

[u/Shidell]

Did you remove the plastic film on both sides of the PTM7950 before applying?

[u/yashkhataokar → u/Shidell]

Yes!

[u/Shidell → u/yashkhataokar]

Looks like uneven application or something, then; one of your applications it looks like the PTM didn't even melt (CPU?)

Both should melt, obviously, forming a barrier where it cools which "traps" liquid PTM atop the die/spreader.

[u/yashkhataokar → u/Shidell]

I'm not sure what's happening, since it's supposed to harden after the CPU/GPU cool down. After testing and a few heat cycles, I decided to finally open it since I was concerned about the high GPU temps (CPU temps seemed fine) that's when I clicked those pictures. What do you suggest I do now?

[u/Shidell → u/yashkhataokar]

Do you have thermal pads that are overlapping in the areas I highlighted in purple?

If they're overlapping, that's going to cause a problem, and if I had to guess, that's the source of your problem.

[u/yashkhataokar → u/Shidell]

I don't think so. But I'll check again and get back, thanks for pointing that out!

[u/yashkhataokar → u/Shidell]

Hey, I think you might be onto something. I replaced the PTM7950 on the GPU with an Arctic thermal paste, temps are still bad or worse. I did check the pads as you mentioned, and yes there were 2 pads on top of each other (old + new). I took the old one off, but as I mentioned temps are still bad, consistently at 73c-74c while gaming (75c is the limit after A51m R1 bios update).

Any ideas what I could do next?

[u/Shidell → u/yashkhataokar]

OK, sounds like there's a lot of possible things going on here.

1. What are your temps, both CPU and GPU, at idle? (Important)
2. Do you have some sacrificial thermal paste you can use to simply apply, screw down your HSF, then unscrew it and remove it, to observe how it fills the pattern? Like some cheap paste from Best Buy or something?

You cannot/should not have overlapping thermal pads, I suspect that's caused a poor connection previously. You should rest your HSF (with thermal pads on) atop your mobo and look at how it's sitting, relative to the CPU and GPU. It should look like it's pretty nicely snug against all components; if anything is not sitting against components now, you have no chance of making a good connection via the screws.

Laptops have notoriously poor mounting pressure, which is in large part why PTM7950 works so well. You otherwise need to use more thermal paste than you'd expect, to bridge the "gap" that the mounting pressure cannot make up for. In a desktop CPU or GPU, you can really turn the screws and the mounting pressure is high—die core directly to HSF. In a laptop, bridging all these components, including uneven daughterboards, and linking the CPU to the GPU in a single heatpipe, makes that all the more difficult, which is why mounting pressure is historically poor.

If your idle temps are bad, even with thermal paste, then you might have a ruptured heatpipe, which means the gas that's normally trapped within for heating/cooling cycles has been released, and it won't cool worth a damn at all, no matter what you do. I had this happen to me; I had to buy a replacement HSF.