8800GTX repair time

[jkenzie]

Well I've never smoked a card before, but I guess there's a first time for everything.
I decided to add the vdrr mod to my card today and got it all wired up, but I made a mistake. I didn't check the stock resistance at the attachment point for referance. Well that was bad. When I fired it up it was showing .81 volts. the computer booted into windows but had no video out.
I pulled everything but no dice, still showed .81 volts.
Can anyone find me the correct value for this resistor? I'm reading 1.38k right now, maybe I cooked it when I soldered the wire.

John

[G H Z]

You can simply turn the VR until the voltage is in the normal range and the card will work normally...but it sounds like you might have other problems.

[STEvil]

should always set the VR to max resistance when modding (unless explicitly stated that you need minimum resistance at start).

Might have put it into protection mode (if there is one on the vddr circuit), but agree with GHZ, dont get your hopes up.

[jkenzie]

Here is some follow up.
Most of the information I was able to find said the VDDR sense leg resistance value should be about 536 ohm's and 1.95-1.97 volts.
That wasn't what I was finding with my card. I have an EVGA super clocked 8800GTX Part# 768-P2-N835-AR. The total resistance value on the sense leg for my card was 315 ohm's and 2.2 volts. So it seems EVGA is already overvolting the ram (can anyone else confirm this?)
So I ordered a 1.37k and 825 ohm 1/16 watt 0402 resistor to get the circuit back to 315 ohm's. Soldered those little buggers in and now the card is screaming again. :up:
I word of warning to anyone with a super clocked card thinking of doing a VDDR mod. If the above is true for all SC cards, a 20K VR will bring you down to 502-501 ohms or about 2.25 volts. That seems a little high to me as a starting point. I wired in a 50k Vr but didn't make the final connection (for future use). The 50K should only bring it down to 512.

Anyway, I was able to take this card to some insane clocks last night.
Stock 621/2000
Over clocked 729/2484
38-40C load temps on water.
John

[nelsmar]

wow nice overclock. what are you cooling with for hte ram... full face? i did block + ramsinks and i think its holding me back. no matter hte voltage 1044-1053mhz is max on my mem ;x

[jkenzie]

I'm using an EK full cover block and a home build chiller that keeps my water temp at 12C.

Here's a question someone might be able to answer for me. I haven't been able to get the card to clock faster than 729 core 1728 shader.
I can scale up the slider in rivatuner and ati tool past 729, but RT and Everest show core clock stuck at 729.
I backed off the shader clock in RT, thinking it was maxed out, but that had no effect either.
Anyone have any ideas?

[Praz]

25k VR (minimum 15 turn) is what's needed for the memory.

[nelsmar]

what drivers and os are you running? i had that problem @ 675mhz with 163.75 drivers. 169.04 if i bump it itl hit 750 core

[jkenzie]

I pushed it somemore last night and realized what was going on. The jumps just get bigger the higher you go. (See chart below) I just needed to push it to 743 to get to the core frequency of 756. I'm stable there but the next jump is 783, maybe a little more than I want to put on my card right now.



Set core | Resultant frequency
frequency | Core Shader
---------------------------------
509-524 | 513 1188
525-526 | 513 1242
527-547 | 540 1242
548-553 | 540 1296
554-571 | 567 1296
572-584 | 576 1350
585-594 | 594 1350
595-603 | 594 1404
604-616 | 612 1404
617-617 | 621 1404
618-634 | 621 1458
635-641 | 648 1458
642-661 | 648 1512
662-664 | 675 1512
665-679 | 675 1566
680-687 | 684 1566
688-692 | 684 1620
693-711 | 702 1620
712-724 | 720 1674
725-734 | 729 1674
735-742 | 729 1728
743-757 | 756 1728

[Praz]

Without using a single-step BIOS that how all GTX cards clock.

[gOtVoltage]

Have you tried upping the Shader with lower GPU? Look in my Sig GTS320mb..I need Volt mod GPU for more action...Now that your fixed ,maybe try the new beta driver and see what you get ...Its well worth the time. Im at 100% stock Volts.

[gOtVoltage]

Yeah all GTS/GTX clock the same....I think the GTX even allows smaller increases but then the higher up in the OC the jump in the MHZ increases will start to increase with each MHZ step too...I also finally Vmodded my card and am very happy with it...

[Timbosan]

I pushed it somemore last night and realized what was going on. The jumps just get bigger the higher you go. (See chart below) I just needed to push it to 743 to get to the core frequency of 756. I'm stable there but the next jump is 783, maybe a little more than I want to put on my card right now.

thats a really nice clock for an A2 revision, on gpu, shader & mem. you said you vmem was 2.2v stock? thats the highest ive heard of yet, maybe it means its safe longterm. I had previously thought 2.1v+ needed better than stock cooling. what vgpu are you at for 756 stable?