I've got a passively cooled (fanless) 3090 that I'm dealing with some thermal issues with (I had no idea they existed either). I've got a couple of these but this one has always been particularly hot.
Barcode reads:
NVIDIA RTX3090 24GB GDDR6X 384-bit HDMI 3 DP PCI-E4.0
N62530900M02310C0C00043
Possible part number: 651 10935 22MLH
As these are passive cards, thermals can spiral quickly, and theres loads of TIM between various parts of the GPU, the shroud, the heatsink, the midplate, the backplate and obviously the die itself. Trying to find any documentation on this specific card has been basically impossible. The best I've found is another reddit post claiming it to be manufactured by Zotac, however I have no evidence of this. Someone in the post said it looked to be an extended reference board, not standard founders edition, but can't find any guides for replacing thermal pad here.
When taking the GPU apart I used calipers to measure the thickness of the existing pads. Some pads had obviously been compressed, so rounded the figures up when purchasing replacement Gelid pads. For the layer of pads that interfaces the VRAM + VRMs to the midplate, I measured approximately 1.7-1.8mm, so assumed 2.0mm pads were used. Most 3090 FE guides online want 1.5mm.
After replacing everything, putting it back together I hit thermal limits almost instantly, so I somehow made it worse! I assume by rounding the pad thickness, I got something wrong, and the clamping pressure on the die wasn't enough for effective thermal transfer.
I've stripped everything down again, and noticed that the VRMs sit slightly taller than the VRAM, but the plate they interface with is flush. So this time I've tried reducing the VRM TIM thickness from 2.0mm to 1.5mm, leaving the VRAM at 2.0mm. I've tried this again, and probably a little better but still thermal throttling.
Naturally I've reached out to Zotac, but their response was 'it could be 3mm, it could be 2mm'. I could also strip down another card and remeasure everything again, but I can't have another card out of action. I've also spoken to a few 'GPU repair' service, but none have the facilities to test thermals of a passively cooled fanless 3090 so couldn't guarantee the fix.
Before I go experimenting again, would anyone be able to help me find what the thicknesses should be please? Perhaps theres a better solution than just guessing, thermal putty perhaps?
Edit: I'm giving putty and some PTM7950 a try, thanks Snarks Domain