Overclock - ATI Radeon HD4850 : too hot, need advices

[Rockz]

Hello

I'm pushing up an old system, and the weak point is actually the GPU.

It's a Connect3D ATI Radeon HD4850 512MB (Dual DVI).

Here is the current install:
- GPU core pencil mod: stockResistance=1.86kOhms, moddedResistance=1.30kOhms; stockIdle2DVoltage=1.08v, moddedIdle2DVoltage=1.16v, moddedLoad3DVoltage=1.25v
- stock BIOS modded with RBE: just updated the frequencies profile (last app tab, "method respecting the BIOS hash integrity", for proper GPU recognition by the ATI drivers), to unlock for 800/1300Mhz max oc settings, in ATI CCC
- GPU speed settings: core=760Mhz, memory=1020Mhz
- an Accelero S1 is attached on it, using Asaka ceramic thermal paste
- memory chips have heatsinks, attached with same thermal paste and electric tape
- 2 x 85mm fan, attached on the Accelero (1 over the GPU core, 1 over the right-end of the card (i.e. the opposite side of the DVI connectors)), blowing outward
- case has a decent airflow: 1 x 85mm fan @ 2800 RPM, attached at front-down of the case, blowing inward; and the same attached at bottom-up of the case, blowing outward. All temps are fine (example: motherboard: 31°c, CPU: E8400 + 6Ghz DDR2 mixed - 55°c @ 4Ghz, cooled with an Hyper Evo), except the GPU that always ran hot

Idle and load temps are quite bad:
- idle (DispIO / MemIO / Shader): 48°C 68°C 52°C
- max. acceptable load (BF3 gaming in 1680x1050; with low/medium settings; DispIO / MemIO / Shader): 58°C 104°C 68°C
- max. load (i.e. until BSOD/reboot; DispIO / MemIO / Shader): 66°C 108°C 76°C

What I think beeing a problem:
- the MEMIO chip is still very hot, and I can't find a way to get it cooler
- the 2 fans attached on the GPU are blowing hot air at the bottom of the case: this air is blocked there, making the area warmer and warmer, and not extracted --> should those fans blow inward, "on" the card ? I could also make some hole in the bottom-down, or down (and laying PC a few centimeters over the ground), of the case, to get 1 fan still blowing outward, and the other one, perpendicular, directing this air and blowing it outside the case

A short history on this 5years-old running GPU: it always ran insanely hot. Before having the Accelero, I couldn't run any game (low settings) with more than 1024/1280 resolution, on stock voltages/frequencies: BSOD/reboot, due to the MEMIO temps. Since Accelero, I can run 1680 resolution, with some settings set to mid/high, but I'm still near the 110°C threshold. It seems those high temps didn't damaged it, but it's bottlenecking it as well.

At the moment, the MEMIO starts decreasing slightly (96°C) if I go on a 1024 resolution. Anything higher pushes its temps over 100°C. Any memory clock higher than 1020Mhz results in a GPU driver crash (not the BSOD/reboot behavior, observed when overheating), so I sat it there. The overclock frequencies are stable (to know this, I check what crashes my system when running both max. ultra 1680 res, and check for any long-run crash when playing on normal settings (low/mid settings @ 1680 res) : if I get a GPU driver crash, I'm too high; note that overclock benchmarks with furmark or so, are not giving any artefact or GPU driver crash, when I go far over the current overclock; but when gaming, the overclock limits show themselves more visible, and trigger crashes when too much).

Goals:
- 1/ find ways to cool it
- 2/ pencil mod it further to reach a 800Mhz GPU clock, eletric tape this, and enjoy :p

This is my first o/c system, to keep money for an Haswell upgrade in 2013.

Thanks for your experience and advices on this one

[Rockz]

Ok, it seems it's a problem with the heatsink not beeing weel in contact with the GPU chip (MEMIO is a part of the GPU chip). I'll try some reseating later (removing the Accelero 4 x plastic circles may do it, but I already had those temps with the stock cooler).

[Rockz]

Aaah yeah, got it cooler

I reseated the Accelero sink, but removing the 4 plastic circles first, and applying a thin and even Arctic Silver ceramic on the whole Accelero plate : now 65 79 66 on max load (and still a BSOD/reboot after this). MEMIO drop down by 25°C/35°C.

If you get this problem on other GPUs, I read that the MEMIO is on a corner of the chip, so putting a thermal paste dot in the center on the chip, hoping the dissipator will evenly apply it, is very likely to fail imo.

I was using Asaka 445 previously btw, and it's quite bad (try to spread it with a finger, and you 'll see it disappears/retracts almost instantly, instead of going white on your fingers; it seems too thin).