Another 8800 GTX volt mod with issues ....

[aussie-revhead]

Hi guys , I just got my water cooled quad / GTX rig going and its all running well except when I activate my volt mod ( via a switch) the vgpu jumps up and the pc shuts down . Luckily it restarts fine and the vid card still works , but what could cause this ?

Do you want to see a pic of my mod ?

:up:

[dengyong]

Yeah.

[aussie-revhead]

Here are some pics, so let me explain -

Pic 1. You can see the volt mods clearly, the extra wires are just a thermal probe behind the gpu . The mod wires cross to the other side of the pcb to a switch arrangement.

Pic 2. I have an on-off-on mini toggle switch and two 500 ohm VRs as I wanted to have a hi and lo mod setting as well as being able to disable it easily , Im certain my problem lays here . The vmem mod seems stable and doesnt have the trickery attached.

When I switched the mod on (with Vr set to 500) the vgpu seemed to spike , showing maybe 10v on dmm, as it moved faster than my dmm could keep up. What voltage should I get at the positive side of the VR ? I will try to attach a wiring diagram .

Pic 3. Wiring diagram of my switch setup.

:up:

[aussie-revhead]

Any ideas guys ? Is it something to do with the two Vrs in parallel ?

:confused:

[oohms]

Actually how come you set them up like that? (in parallel, with all 3 legs of the other pot connected?)

[Praz]

Are you changing switch positions with the system powered up? If so that is your problem. Put the switch in whichever position you need before starting the system.

[aussie-revhead]

Actually how come you set them up like that? (in parallel, with all 3 legs of the other pot connected?)

Hey man , sorry I didnt have the time to finish labelling the diagram , thats a toggle switch . I was shooting for something different , that would give me two mod settings (as in my op). I might just cut one out and try it. I did switch it over with pc running , but Im pretty sure I tried it before boot too and it didnt like it at all .

I just tried it again with switchover done before bootup and it is showing 2.5v vgpu , no wonder ovp is kicking in and lucky then I didnt eliminate it yet. I better try cutting out a VR .

Thanks guys .

[oohms]

Ok that makes much more sense now :D

Have you measured your resistances with the mod soldered in?

[aussie-revhead]

Hey , nice blue tongue !!!

Yeah I just did some tests on it before and from the gpu mod point to earth without the mod activated its about 465 ohms or there abouts . With a 500 ohm VR activated that resistance drops to about 250 ohms . This seems like a very large drop , though the specified 500 ohm resistor would do that right ? Do I need a larger resistor ? What else could be so wrong ?

:up:

[oohms]

Thanks!

Wow you are using a way too small resistor :eek:
Rule of thumb is 20 times the resistance between the mod point and ground, set to max before you solder :D
(so for 465 ohms your looking at a 10k VR)

[aussie-revhead]

OK thats easily fixed then as I have a 10k spare .

I will get back later when I apply this .

:up:

See here , thats what is being used on this forum afaik .

http://www.xtremesystems.org/forums/showpost.php?p=1839559&postcount=5

[oohms]

Kinda odd.. hmm

Well if its too big it won't hurt, you'd just get close to stock voltages, and turning the trimpot wouldnt affect the voltages much (until you get to the very end of the pot, and the resistance is close to zero, watch out for that!)

[oohms]

Are you sure you measured it right? They say that the stock resistance is only 33 ohms in that thread

[aussie-revhead]

lol probably not eh , I will get back to it tomorrow as I have an assignment to do . Wasnt 33 ohms across the resistor ?

:up:

I know this is for a gts but this guy seems to have my exact problem:

http://www.xtremesystems.org/forums/showpost.php?p=2443365&postcount=213


I had put 503ohms and i obtained.... 2.46v
972ohms = 1.84v
503ohms = 2.46v

so I will try to put a 10k vr set to 2k

EDIT : it's ok I have 1.60v with 2k... i'm actually at 1.45 stock cooling...

:up:

[Timbosan]

I have a GTS but its a very similar. its a strange mod - the resistance of the mod point to ground does not change from 33 ohms when you turn the VR in my experience. I just trusted myself and set VR to 20K, and to my surprise as i turned the VR the vgpu rose. A 20K is too high and nothing happens till you reach the last 25% of the VR, then its very sensitive. Use a 10K tuned to 8 - 10K before soldering on :up:

[aussie-revhead]

Thanks Timbo , so 10k on my gtx should be right eh ?

Cheers mate .

:up:

[Timbosan]

Yeah it would be the best choice i think :up:

[BenchZowner]

What voltage do you get with the Vmods on and what voltage with the Vmods off.

A "single" high voltage jump in real-time might "activate" the PWMs' controller protection, resulting in a lock ( due to power supply cut-off ).

Just a quick thought ( didn't read all the trimmer connection details yet )

[aussie-revhead]

BenchZowner - vgpu is about 1.27v idle and 1.21v loaded without vmod , and when I clock in the vmod it jumps to 2.5v !!!! I tried this before boot and watched vgpu as it posted and it showed the same . With 1.27/1.21 its stable up to 660 mhz ( 648 actual - just below next clock jump )

Thanks Timbo.

:up:

[BenchZowner]

Even after re-looking at your drawings I can't say that I have a clear picture of what you've done.

From what I 'get' out of your posts is that you want to have your 8800GTX Vgpu & Vmem modded, with the ability to enable/disable the modifications.

What you should do is use two different switches...or even two "headers" from a CDin cable ( the ones that we used in the past to connect the CD-ROMs to the sound card/mobo's codec to have the mods removable.
You'll use the header to connect the VR's pins, you won't be soldering the cables on the VR, but on the header.
Easy to plug, easy to remove.
Same could be achieved with the switches, one switch for each mod.

However, you should not enable/disable the Vmods in real-time ( while the PC is powered up ).

The VR's required for the mods are a 500 Ohm VR for the Vgpu, and a 20kOhm VR for the Vmem.

[aussie-revhead]

... you want to have your 8800GTX Vgpu & Vmem modded, with the ability to enable/disable the modifications.


The VR's required for the mods are a 500 Ohm VR for the Vgpu, and a 20kOhm VR for the Vmem.



You got it mate , three position switch giving gpu std volts, mod-lo and mod-hi . I might have to ditch this , but why do I have 2.46vgpu ? I had the vmem mod on the switch too but it seemed to be leaking voltage across so I hard wired it .

:up:

[aussie-revhead]

OK guys , I cut out my gpu VRs and went and bought a bunch or resistors ( as they didnt have any VRs at my local electronics store) . Now my switch setup is working and I have a lo-mod voltage of 1.372 unloaded and 1.315 loaded . Hi-mod is 1.57 unloaded , yet to test loaded voltage.

By the way the resistors are 5.7k and 1.8k , so Im not sure where the 500 ohms comes in .

Cheers .

:up:

[Timbosan]

Good stuff, glad its sorted :up: I told ya the 500 ohms is too low, thats why you got such a high voltage (hence why i said use a 10K). I have no idea why it was recommended to use a 500 ohm.

[aussie-revhead]

Thanks Timbo , yeah I checked back through the volt mod threads to be sure I didnt get it wrong , but its working now so its all good . With a tiny 0.100v increase its stable at 690 core now , so my gtx has gone from a very average example to a healthy one . I have the hi side mod set to 1.58v as a benchmark only setting and if I can get 750 core I will be very happy .

:up:

Unfortunately for me it seems I have a very average card , initial testing with 1.35vgpu was good at 690 mhz , but with 1.55 it only does 711. I still have not increased vmem yet , and havent run the quad above 3.6ghz , so there is a little left yet.

Cheers .

Dengyong - how do you get such a huge score with moderate cpu clock and a little more gpu than me ? ORB says your using server 2003 , is that correct ? Does 4GB help ?

[dengyong]

My cpu is at 3.8ghz and I'm using xp64 to bench (tri boot) I don't think 4gb ram makes a difference.

You won't gain much past 1.5v core. I've been using 1.5vcore 24/7 for 11 months with no problems.

I use a 1k ohm 15 turn vr for vcore.

What operating system are you using ?

[aussie-revhead]

XP , but it doesnt matter now as I have moved on to a 512GTS .

:D

[_Stelios_]

Hello XS,
I had the same EXACT issue on my gtx..
The weirdest thing in my case was that i modded it with a 500ohms vr and the mod worked just fine for the first day. The next day when i tried to put the mod on again [i'm using jumper for setting the mod on or off] the card immediately turned off. I even tried to turn the pc on while the mod was set in on possition and the vgpu reading was 2.5x :shocked:
Should i replace the 500ohms one with a higher resistance vr? :shrug:
Why is this happening? :confused:

[aussie-revhead]

I did my own testing with fixed value resistors and chose two that gave the voltages I wanted . I would test with a higher value VR or add a fixed resistor in series if possible to help testing.

:up:

[_Stelios_]

I've replaced the 500ohms vr with a 10k one and the mod works ok now...
But i'm still wondering why the first day on mod point i read 33ohms and the second day i read 45x ohms.. :confused: