gpu strange fan issues

i have sapphire HD 7870XT Dual-X. both fans was spinning in the first two years from buying the card. after that i started to notice that the second fan doesn't spin unless fan speed at 78% or above. i guess it happened after i installed Crimson driver. but that doesn't matter as i get used to it, and one fan seemed to handle the graphics card.

what is matter that after a couple more years and after i replaced my old thermaltake 450w PSU with FSP Hexa 500w, i've noticed that even the other fan doesn't spin at idle unless temps are above 42c (48c now). and the moment i stress the gpu with furmark or with a game it goes down instantly to 0 RPM (i don't know why?) until 78% then start to ramp up again with the other fan. suddenly from 0 RPM to 3000's RPMs!.

even with the fan curve set it to ramp before 78% it doesn't.. thats in gaming or stressing only, which is strange.
i can ramp it up before 78% but with no stress on gpu. and it will turn itself off when temp is at late 30's or after a few minutes at idle.

i just need any explanation for why the moment i stress the gpu the other fan that used to work all times goes down to low RPMs until its 78%?.. and why it doesn't spin at idle unless temp is above 42, then when temp decreases to mid 30's the fan turn off again, and so on..

i haven't installed any new third party programs before that happened and i haven't installed any new drivers.. the cause seems to be deeper than just "faulty fans". because if it just a dying fan it will act randomly. but it seems that its being controlled by something. although this issue happens in the bios.

Edited by whiteknights, 18 November 2017 - 02:20 AM.

Since dual fans on GPU's are usually wired in parallel (usually to a single fan header) rather than independently controlled, this doesn't make a lot of sense to me.  There's no reason for them to be independently controlled because they are both attached to the same heat sink.

All I can suggest is using the software (I think you can do this within the AMD driver) to manually set the fan speed to 100% at all times, and observe what happens.  If one is clearly spinning faster than the other, or not spinning, then my best guess would be one or both fans are faulty.

thank you for your help.. i did set the fan speed at higher RPMS, they both seems to spin at same speed, but i've notice that the fan which had the recent problems is making rattling sound when its lowering its RPMs starting from 2000 to 0. and the fan seems to have trouble working at lower Rpms.. i have to set it at higher ones so it can stay constant.

also i have a small doubt that it could be a psu issue or a bad 6pin pcie connector because i started to notice the other fan problem after upgrading my psu.
and it happened 3 times when i switch my 2x6pin connectors i get blank screen but windows start normally, i have to switch them back so i can get a signal, i don't know if that could be normal?

it made me suspect that it could be related to the fan issue, and i want to eliminate the possibilities.
i also suspect that it could be VGA bios problem, and i fear it could be a faulty fan controller that built in the GPU.. that might explains why every time i stress the gpu, fan goes down to low rpms instantly. built in fan controller might have trouble controlling the fan.. or maybe GPU bios got corrupted.

Edited by whiteknights, 19 November 2017 - 09:45 PM.