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Sapphire HD7970 VAPOR-X/GHz/6GB voltmod

post #1 of 3
Thread Starter 
Hi there, long time lurker, time to start a thread since I've found so little about the Sapphire cards.

So, a while back I got a HAF-X and started out with a Sapphire 7970, 6GB version since I intended (and do) to game in Eyefinity + aux monitor so I figured I could use at least half of that RAM smile.gif. Then I just had to add a second 7970 and that has been good for 60+ fps in Eyefinity for most games, but it got quite hot in there and the fans where killing my ears. Now it's WC'd, bummer though that Sapphire is the retarded cousin of all the 7970 PCB's which seems to be the only one not having a full cover block, so I had to go with the EK VGA Supremacy. It works though. Also a bonus was that the Sapphire cards already have heatsinks on most components around the VRM etc. When I went from air to WC the load temps unbelievably went from 70C (lower)/80C (upper) on 1.256V/1175MHz/1550MHz down to 45C for both cards! This makes me wanna fill that headroom with some performance!

The problems/challenges then.The Vapor-X back plates on the stock card, the upper card, is getting really really hot to the touch. Since Sapphire did not add VRM temp monitoring available through software I have no idea what they get to, so first of all - would it make sense to add an external USB temp probe (thermocouple/thermistor of some kind) to the VRM sections if I plan to raise the GPU voltage more than the locked 1.256V? And if I would, where would the best place be to thermally attach it?

Also, to the mod. I guess I'm just gonna start with the GPU voltage (I've been able to test short unstable sessions on 1225MHz which has yielded an increase from say 55 to 60fps relatively). Now Sapphire has of course made the CHL8228 section of the PCB totally different from every other 7970 card. From what I could measure though, the VSEN pin has got 6.3ohm (w/ DMM probe resistance subtracted) to GND and VRTN has some 3ohms to GND. I would have guessed it would be much less resistance on VRTN. The question though is why they made it this way while all other VRM sections I've seen seem to have more in the range of hundred's of ohm's to GND at least? Anyhow, I take it I can still put a potentiometer (I have some 500ohm/15 turn pots I was gonna use) on VSEN and if the max voltage I come to now is 1.256V I should get something in the range of 1.27V with the pot set to 500ohm's initially. Or am I foreseeing some smart thing about VRTN having 3ohm's to GND?

Can post pic's of the PCB's when home if interest exists. Never seen a Vapor-X VRM section pic being posted anywhere else.

post #2 of 3
Thread Starter 
Update! I have now successfully soldered/glued it together and I can confirm it works. The two cards had pretty different feedback resistances to GND, one 6,3ohm and the other 5,9. Nonetheless, it works very well and with 475ohm (pot's maxed) inserted I got almost a 10mV boost, and of course leaves quite a bit of headroom now. Under load in Xfire the main card has 1.285V (1.278 w/o mod) while the bottom has 1.245V (1.236 w/o mod). I would have guessed them to be much closer to each other in voltage. Doesn't matter though, now I don't have to rely on strange BIOS'es or AB for voltage control!

The RC connectors were quite handy, especially since it makes it super easy to install/remove entirely to make the cards "stock" again. Here's some pics of it all (pretty high res. if you wanna use it for reference):

All in all I'm happy!
post #3 of 3
hi everyone...with this psu ... http://www.e-shop.gr/product?id=PER.640316 can i run gpu that requers more than 8 pins?thanks
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