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My failed 7870 XT Mod

Discussion in 'Cases, Modding & Electronics' started by silkstone, Jul 7, 2013.

  1. silkstone

    silkstone

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    So, after getting a 7870 myst edition, I figure I will try to sort out the High VRM temp issue.
    I was getting temps of around 72 core 73-74 VRM when using the Heaven benchmark tool at 1200 core.

    As the Powercolor Myst edition only has one fan, I figure that I can easily remedy the situation by taking off the shroud and attaching 2 x 80mm fans, replace the TIM and use a different thermal pad on the VRMs.

    Deepcool fans are the only ones I can get hold of that aren't 120mm, but I figure that they are advertised at 26CFM each at 12 V so they should work well enough.

    [​IMG]

    A bit of sleeving later

    [​IMG]

    Then I go to remove the shroud and fan from my 7870 and disaster!

    [​IMG]

    I really should have known better than to use pliers. :banghead:

    I carry on ahead, hoping that it'll work well so I won't have to worry about the broken cable on the original fan. I get the fans mounted along with some Xigmatec Freezing point on the gpu and some EK 1mm thermal pads on the VRMs and mount the whole assembly on the card.

    [​IMG]
    [​IMG]

    Time to test it.
    The GPU temps hold nice and steady at around 70 C, in Heaven, not awful, but not a great sign as I was expecting a little more. I scroll down to the VRM temps and watch them gradually rise to close to 100 C.

    Failure :cry: the fans just don't move enough air in the right direction to cool the VRMs properly. I tried putting the original thermal pad back on the VRM and re-test to get the same result. I tried moving the fans to be sure that the VRMs were directly under them, again no go.

    So in the end, I solder the broken cable back together and force the (now bulky) pin back in the fan header. Re-assemble it all and test it out.

    Temps are now at 73 C GPU and 79 C VRM. I'm going to see if the ek pads take some 'burn in' time before trying to reapply a new cutout as a loss of 5-6 C was the opposite of what I was going for. :ohwell:

    Does anyone know what the cable I cut, did?

    I'm not sure whether to try again with 120 mm fans that I have lying around. If I try again, could anyone give me any advice for what I should be looking for in a fan?
    Last edited: Jul 7, 2013
  2. james888

    james888

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    The vrm's do get hot on these. 79c is fine though, I think they can get to 110c before problems.
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  3. natr0n

    natr0n

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    Use a game based benchmark. I use Lost planet 2.

    Heaven and others like it over stress your card beyond what a normal game does.
    you can add a 3rd fan for better cooling of vrm.
    you cut the pwm cable.


    You could add some TIM on both sides of your vrm thermal pad.
    Last edited: Jul 7, 2013
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  4. silkstone

    silkstone

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    I keep a log from FC3 as well, It also gets to 78-79 C.

    I just re-checked my logs, and it seemed to balance out at 74 C for 10 mins with the original thermal pad. So, 78 C at the moment isn't that bad. Although I am considering taking it apart again and replacing the pad with the old one.

    I don't think a 3rd fan would make any difference, even when one of the fans is dierctly over the VRMs, not enough air is getting down to them. I do have an old, ridiculously strong 92 mm fan that I am thinking of trying though.
  5. natr0n

    natr0n

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    The 92mm would make a big difference.Noise would be only issue.
  6. Jstn7477

    Jstn7477

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    Umm, that's a Pitcairn chip, and that VRM heatsink is incredibly tiny. Have a GPU-Z screenshot?
    Crunching for Team TPU More than 25k PPD
  7. silkstone

    silkstone

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    I put the original thermal pad back on, same results now. 78 C, but possibly going higher . . . I need to monitor it a bit longer to see.

    [​IMG]
    [​IMG]

    (It's a Tahiti XT chip btw)

    The 92 mm fan is really noisy, making the lack of pwm on it a real issue. One of the reasons that I wanted to do this mod was to stop my video card from sounding like a jet engine when playing games.
  8. de.das.dude

    de.das.dude Pro Indian Modder

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    ahh, if i had known earlier, i would have helped design heatsinks. i am a senior in mechanical engg, and we covered heatsink design and heat transfer in the 3rd year :(


    scratch that.

    i see you are using thermal pads... have you tried... copper shims with TIM?
    might even try arctive silver epoxy.
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  9. silkstone

    silkstone

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    TIM on the GPU but a 1 mm pad on the VRMs. I think the pad is there as a cushion against the thin Heatsink on there. The VRMs are small and look to be easily damaged by the heatsink. They are about 1 mm by 2 mm so any kind of epoxy is a no-go.
  10. Brusfantomet

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    try 7 volt on the noisy fan, could help get the speed (and noise) down)
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  11. silkstone

    silkstone

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    I'm thinking of doing that. The fan has a back panel controller.

    Just to confirm. The little things behind the heatsink in the red box are the VRMs, right?

    [​IMG]
  12. Jstn7477

    Jstn7477

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  13. silkstone

    silkstone

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  14. Jack1n

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    Its a Tahiti LE actually.
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  15. DarkOCean

    DarkOCean

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  16. Jstn7477

    Jstn7477

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    Sorry, didn't realize they repackaged the die onto a different substrate, though I guess that makes sense now if it fits on what looks like a 78xx PCB. It's a shame TPU doesn't have a review of one as most of the other review sites suck and don't even tear down the card.

    My bad.
    Crunching for Team TPU More than 25k PPD
  17. silkstone

    silkstone

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  18. de.das.dude

    de.das.dude Pro Indian Modder

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    no no no.
    the chips is more sensitive. vrms are typical mosfets. they use pads because vrms are not made very strictly, so they are of varying lengths. also soldering may lead to little bit different height.

    i used an ample amount of TIM on something, and it worked, better than the pads. was a long time ago, so i cant remember what it was.

    and anyways, most of them are rated for around 115C.
  19. Velvet Wafer

    Velvet Wafer New Member

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    using MX-2 instead of a pad yielded better results, in these kind of cases ;)
  20. de.das.dude

    de.das.dude Pro Indian Modder

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    yesH!!
  21. McSteel

    McSteel

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    Perhaps you could try somehow directly connecting the VRM FETs to the main (GPU) heatsink? The tiny heatsink resting on them isn't increasing the heat dissipation surface area by an awful lot... Changing that unfortunate fact seems more important (and more productive) than getting more raw airflow. Does the VRM heatsink touch the main heatsink in any way already?

    In fact, you could also use the solder side of the PCB to slap on a heatsink of some sort, directly below the VRM FETs. Use the thermal pad to prevent shorting out anything. I doubt Powercolor used more than 3-4 layers for that PCB, so it should help significantly, if your case has any appreciable airflow through it.
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  22. Vario

    Vario

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  23. d1nky

    d1nky

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    no wonder the temps got worse, like said before. thats the same vrm heatsink on the same vrms kicking out the same temps!

    if i were you id get a bigger heatsink for them, thats a tiny sink which wont dissipate much heat. and modding the fan probably restricted airflow to them.

    you posted a pic of exactly what needs changing/modding! and by the counts of it, 4 chokes = maybe 4+2 or 4+1 phase design.

    change that damn silver sink on the driver mosfets and stop wasting time on the core.
  24. mm67

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  25. badtaylorx

    badtaylorx

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    the VRM area is quite thin tho....you'll hafta cut that watercool one down to size a 'lil...

    i did one last year with Koolance and Alphacool blocks...

    [​IMG]

    [​IMG]
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