260 gtx OVP

[Chainspike]

Hi,

I have a 260 gtx 55nm Rev.1 NCP5388. I already ran a VR from pin 19 to ground. MOD worked good up to about 1.22v when OVP kicked in stopped me. I have shorted out the resistor between pin 12 and 13 and disabled the OCP but this had no impact on the 1.22v limit wall. How the hell do I disable the OVP. Don't tell me its impossible if they have already done it on the 285 and 275. Below is a link to the NCP5388 datasheet.

http://datasheetz.com/ONSEMI/NCP5388-D/NCP5388-D.html

After reading sheet only can find this in it.

Overvoltage Protection and Power Good Monitor
An output voltage monitor is incorporated. During
normal operation, if the voltage at the DIFFOUT pin
exceeds 1.3 V, the VR_RDY pin goes low, the DRVON
signal remains high, the PWM outputs are set low. The
outputs will remain disabled until the VCC voltage is
removed and reapplied. During normal operation, if the
output voltage falls more than 300 mV below the DAC
setting, the VR_RDY pin will be set low until the output
rises.

That tell me that when pin 17 (diffout) hits 1.3v (vgpu) it shutdowns the card. ERRRRR... So only way can see to kill OVP is to some how fool pin 17 into always having a lower voltage then 1.3v. I can see doing this by increasing resistance in the pin 17 circuit. Question is how much resistance and where to solder it to.

[CryptiK]

Measure resistance of pin 17 to ground. Multiply this by 20, and solder a VR of close to this value between pin 17 and ground. Tune VR to max resistance before soldering in. Tune down to raise OVP voltage trip point.

Should work, I accept no responsibility if you fry your card etc etc

Sounds to me like if the card is crashing under load, it's OCP that is being triggered not OVP. OVP can be triggered at idle by simply raising voltage with no load. OCP is usually triggered under load.

EDIT - have you verified with a DMM that resistance between ROSC (12) and ILIM (13) is 0 ohms? If it is OCP should be disabled.

[Chainspike]

Alright I'm back. Ohm between pin 12 and 13 is 0. I double checked it and gave me zero again. So ocp is disabled. I still get when switching to a 3d app black screen shut down, so ovp gotta be kicking in. In the process of soldering a wire from pin 17 to a VR right now. Pin 17 is a bizach because only thing I can hook to is a tiny resistor in the middle of a buncha stuff. So taking my time with it and making sure everything is perfect. I got a resistance of 7.64 k ohm and I am going to install a 150 k ohm VR from pin 17 to ground. Kind of cool that its like how I thought it would end up to shut off the OVP. Very similar to the 285's 100k ohm VR to ground.

[Chainspike]

ok, I got a wire connected to pin 17 and to a 100k VR. My problem is still running smack into the OVP even with the resistance down to 5k. I checked ovp again and resistance is still 0 between pin 12 and 13. I checked the resistance on pin 17 and it is lowering down to about 4 ohms but still hitting OVP at 1.24. I 'm not sure if a vr between pin 17 is gonna cut it. I'm going to keep lowering it down see if can get it to accept 1.24v

[Chainspike]

This is my problem also. It posts fine runs to windows fine. I start 3d app and boom black screen, vgpu drop to 0.

[CryptiK]

Something else may be going on, as the card technically shouldn't trip OVP until 1.30v. I don't have time to further study the datasheet at the moment but have another look at it if what I suggested for OVP mod doesn't help.

You could try triggering OVP with card at idle by increasing voltage past 1.30v - it should shut down. Then lower resistance between pin 17 and ground then try it again - it should shutdown higher than 1.30v. If this works, the OVP mod works, and what you are describing now at 1.24v is some other form of protection kicking in (OCP not fully disabled, temp etc).

[dejanbinladen]

any news about this mod.. i soldered VR on pin 19 and got prety nice voltage boost then disabled ocp by shortening 12-13, but i think OCP is kicking no matter what , i have idle about 1,22V and load 1,27-1,28. OVP is no problem to me cause i tried it on stock and the card shuts down, but in vantage i just go back to desktop and driver fails... thats about 792mhz for gpu, and for 786 i am stable...could this be the max of the card ?!?!?! i run 774 on stock voltage it cant be ?!?!? temp are max of the max 50 under load... any tips thanks

dejan

[Mutant_Tractor]

Bump, would be really handy to have this mod,
My GTX 260 doesnt want to even run vantage @ 720/1500/1200 @ 1.24v tried up to 1.288v but no luck :/

OCP modding it now...