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Vmem Modification

It is a peculiarity of 5900 series graphics cards that they are more sensitive to GPU overclocking than to memory speedup. Roughly, you have the same performance gain from an extra 1MHz on GPU as from extra 10MHz of the memory clock rate. Anyway, each jot of performance is important in the race for records, so we also performed a Vmem modification.

Due to mysterious reasons, a majority of those who attempted this mod couldn’t get a single extra megahertz of memory frequency by adjusting Vmem, irrespective of the memory manufacturer (Samsung or Hynix). I can’t explain why I succeeded where others failed – the modification recipe was the same. Anyway, you may try it – maybe you’ll be lucky?

The 5900XT graphics card carries two Intersil ISL6522CB chips. One of them controls the GPU voltage, as we already know, and the other does the same with respect to memory. So, the second mod should be analogous to the first one.

Yes, we do the same: a 10kOhm variable resistor between legs 5 and 7 of the ISL6522CB. To be precise, between leg 5 and “ground”, but leg 7 seems the best ground to me in this case.

Monitoring is performed at the front side of the board; it’s easier to solder a wire there than poke your multimeter there each time.

As concerns the nominal voltage, it differs from 2.5v to 2.85v in different cards, so don’t be surprised to find it “non-standard”. I don’t have any statistics concerning brands, but my Sparkle had Vmem = 2.7v.

So what did I get by increasing Vmem? Until 3.1v the changes were insignificant (some extra 10-15MHz), but after that there was some growth. A memory voltage of 3.4v produced 1GHz memory frequency. On the other hand, from 3.2v on, the memory chips suddenly increased their heat generation: at 3.4v Vmem, one minute of testing in 3D made the chips heat up to 70°C even with intensive air cooling and this temperature soon produced image artifacts due to the trivial overheat. So, we needed to cool the memory chips somehow…

 
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