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How-to: Pencil mod your HD 3870!

Discussion in 'AMD / ATI' started by Random Murderer, Jan 2, 2008.

  1. Random Murderer

    Random Murderer The Anti-Midas

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    Ok, false alarm. I'll be redoing the hard mod here in a day or two, as I have some extra trimpots.
    What happened is apparently I broke a 6Ω resistor while performing the mod. When i tried to boot with the card, I received beep codes saying no video card was installed, so i shut down and pulled the trimpots off. Then I realized I could fix it, so I did, but no trimpots anymore... :ohwell:
    The card is alive, but still on a pencil mod for now.
  2. largon New Member

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    The accuracy is not really about the amount of turns. It's about the resistance change per degree of turn. 500kΩ (500 000, not 500) has 5× the resistance change per º compared to 100kΩ. 500kΩ VR will become very inaccurate after a certain point is passed.
  3. Reset

    Reset New Member

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    The more turns means the less resistance change per degree during a turn, so it does have something to do with accuracy. I just forgot to add the K but I know what it means and the idea is still the same. Could be M for mega/million ohms too.

    The more turns the finer the resistance change during adjustment. So all I'm saying is the more turns makes the VR trimpot more accurate no matter what the total resistance. Although the larger the resistance the more turns you would need to make a smooth transition. Less turns needed for lower ohms. The larger the resistance pot may become less linear closer to the extremes, but I don't know that for sure, and it really shouldn't make a difference in the perfect world!

    But for sure, if the 100K ohm and the 500K ohm potentiometers have the same ammount of turns, then the 100K ohm will be more accurate and fine tuning. Also since a trimpot uses mechanical function to adjust, that makes it more possible for inaccuracy. Now I got a headache -- Thanks largon! :D
  4. Threeflow New Member

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    I know someone...

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  5. trog100 New Member

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    i wondered how they got those core speeds.. my first pair of HIS early 3870 cards wouldnt run 850 core gaming stable.. they are either selected cream of the crop chips or being fed a little more voltage..

    when u get it grab the bios using winflash.. i would be curious to have a look at one.. nice card with nice cooler.. worth the little extra i recon..

    just for the record i used the pc case for the earthing point while measuring voltage.. its easier..

    trog
  6. Cold Storm

    Cold Storm Battosai

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    You all most killed my card man! lol.. Not mad, just glad to see i can still get on here! I still trust you on one condition... You eat before working! I want you mind to be at full thought process... no more of what happened!
    Random Murderer says thanks.
  7. Random Murderer

    Random Murderer The Anti-Midas

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    Lawzorz!
    Ok, I can deal with that.
  8. Cold Storm

    Cold Storm Battosai

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    I hope you can! or this system isn't your test system anymore! my wallet may look fat but is flat...
  9. thoughtdisorder

    thoughtdisorder New Member

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    LMAO - Storm I NEVER saw that bottom lip of yours dragging so low as it was lastnight!:nutkick:
  10. Cold Storm

    Cold Storm Battosai

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    RM has the ability to do it! I know he does.. just got me on what happened... he fixed it! lol
  11. ace80

    ace80

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    I'll upload the bios here as soon as i get it, eta is monday so i should receive it tuesday.
    Yeah i thought the little extra was worth it, kinda neglected my vid card upgrades for a while. I love the iceq3 cooler, i just hope there's some oc'ing head room before i decide to pencil mod it. Don't think i'll be hard modding it thats how i killed my x800gto2 :cry:
    I use the case for the earth aswell but thanks for refreshing my mind.

    While i'm here whats the best atitool version to use with 3870 so i'm ready to go?
  12. trog100 New Member

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    i wouldnt use it.. not fully sorted yet for the 3xxx cards.. the CCC overdrive works without a problem.. the rivatuner monitor is perfect for checking temps and stuff..

    your 850 bios should open up beyond the normal 885 clocking option.. the cooling on your card should be set for higher a fan speed as well.

    some say the tool works but it just made my card unstable.. i dont think it ups the voltage from 2d to 3d properly..

    trog
    ace80 says thanks.
  13. tigger

    tigger I'm the only one

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    Trog,what program do you use to look at the bios's?

    Is there any way i can get ccc to go over 770 with my card on the gpu overdive?
  14. trog100 New Member

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    i use something called "beyond compare" to compare one bios with another..

    the max setting in the CCC goes up when a higher clocked bios is used.. the 850 clock on the HIS turbo 3870 for example should shift the max setting up from 885 to 1500..

    i assume the 3850 card word work the same way..from what i gather the 3850 card simply comes shipped with a lower bios set gpu voltage which limits the clocks by default..

    there might be some speed binning with the chips but other than that they are the same for both cards..

    trog
  15. Cold Storm

    Cold Storm Battosai

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    just let it stay and be... you want the air to move so it can blow off any access lead that might be there. The lead will stick on there. its still there after the first time he did it.. and mine was the same...
  16. tigger

    tigger I'm the only one

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    Heres a nice pic of a 3850 volt mod.The yellow wire is vcore measure,and the jumper disables the vmod.

    [​IMG]
  17. Source New Member

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    Very Nice, any chance you could do a close up with some light on that bottom right corner. I like the jumper idea.
  18. Random Murderer

    Random Murderer The Anti-Midas

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    it's not his, that's a pic from a guy over on xs.
  19. trog100 New Member

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    about that lead sticking.. i did the second mod.. lead between to pins on the board surface.. a very slight roughening of the surface between the pins gets the lead to stick in a normal pencil stroke way.. no piles of random dust..

    two or three light strokes is more than enough.. u lightly apply.. measure the voltage as soon as the machine boots.. if its too high hit the off switch and brush at the pencil to get some off..

    there does seem to be some over volt protection cos mine refused to boot several times.. the highest it booted at was 2.5 volts..

    just over 1.4 is a safe place to aim for.. its very hit and miss mostly way too high..

    a small stiff artists brush is good for dropping a too high attempt.. u can do it with the card still in the machine.. brush off too much and u have to take it out and start again..

    doing it my way is the opposite to all u read.. its all too easy to get too much.. no rubbing like hell to get anything..

    trog
  20. tigger

    tigger I'm the only one

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    Correct,its not mine.I never claimed it was did i?

    This is how i see the jumper connections-

    [​IMG]
    Last edited: Jan 14, 2008
  21. Random Murderer

    Random Murderer The Anti-Midas

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    I wasn't calling you a liar, calm down.:toast:

    Yes, yes, that's correct, the yellow wire is the measure point and the red and black when jumped together complete the circuit to the trimpot.
  22. tigger

    tigger I'm the only one

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    sorry random,if my reply was a bit curt.

    It is a pretty nice way to do it tho'

    heres a rather nice 3870 one too-

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]

    That is a fine piece of work.
  23. Dr. Spankenstein New Member

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    Just saw that one over @ XS as well. Very clean work! I would love to find those clips he's using for the pots...
    Is there something that is used to adhere the wire to the PCB?

    About ready to "grow a pair" and hard mod these puppies!
  24. tigger

    tigger I'm the only one

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    When you realize how thin those wires are,its either good soldering or glue etc.
  25. Reset

    Reset New Member

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    I would guess that thin wire is probably solid core telephone wire. Stranded wire doesn't hold it's shape as well. Telephone wire might be the best to use because it stays the way you bend it and it's thin.

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