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geoffrey 3rd December 2006 12:36

Replacing onboard crystal
I've been modding a cheap nVidia 6600 (non GT) some time ago. Picture of the card (warning high res):

Since pc parts always work with a clock, there must be a oscillator somewhere. Cystals have been used for many years now when it comes down to high precision oscillators. But just because it is a crystal, it is not possible to switch it's frequency just by soldering an extra resistor on your hardware or anything like that. You will have to replace the crystal. And so I did ;-D

My nVidia 6600 videocard has one crystal with a frequency of 27MHz, but yesterday I came across an old ATI Rage wich had a 29MHz crystal. I took both crystals off and soldered the 29MHz crystal back but on the nVidia 6600 this time. And... the card booted :woot:

First thing I noticed was that in fact some changes were made. My TFT is set to it's maximum resolution: 1600*1200 60Hz. After the mod I got a message: "frequency out of range". With Windows safe mode I could set a lower resolution and get into Windows XP again. So changing the crystal atleast did something.
After that I opened a bunch of software tools to overclock my videocard. The programs all red default card clocks. Before I did this mod I got a 3D Mark 06 score of 981 3D marks. After the mod I gained about 100 points with the same clock applied in software. I'm still further investigating what is happening here, but it's remarkable that I got a very decent performance boost. I will come back with a lot of info, but until then, does anyone know what this mod exactly does? Will it only change some basic clocks like the core clock without the software being able to read it, or would the whole card get a little boost (even the core's internal clocks wich I can not read)?

geoffrey 3rd December 2006 17:03

2 Attachment(s)
Here is what I got:

jmke 3rd December 2006 17:12

at overclocked speeds it doesn't seem to offer a noticeable performance boost, but at stock speeds... wow.. where did you get the idea & info to do this? :)

geoffrey 3rd December 2006 17:12

By changing the crystal the 6600 got about 5~10% faster in synthetic benchmarks. But wih overclocking we see something differant. The 6600 with 27MHz crystal seem to overclock much further then with the 29MHz crystal. In our 3D Mark 2001 Nature test this is enough to almost equilize the 29MHz crystal equiped 6600. The small margin is neglictable.

I have a 32MHz crystal ready to pick up next week friday, stay tuned.

geoffrey 3rd December 2006 17:14

I saw Hipro5 @ XS talking about this. I've never heard of anything like this, but my thought: why not just try it out :)

Sidney 3rd December 2006 21:46

Crystal is before PLL days; cheaper to produce too. I remember a similar talk with my youngest brother when he was in electrical engineering school back in 1983. Harmonics in frequency response -

Good to experience with things around :)

geoffrey 9th December 2006 16:29

Crap, with a 32 MHz crystal my screen stays blank even after boot. Nothing wrong: after some seconds I here my speaker playing that nifty Windows logon sound, but to bad I just don't get anything on my screen. Well... back to the 29MHz it is :)

jmke 9th December 2006 16:41

not sure it's a good thing to OC that part of the vga;)

geoffrey 9th December 2006 16:50

9% performance boost in every synthetic benchmark. Using Rivatuner might be a better smarter thing to do :p Heck, I know what it does now :)

jmke 9th December 2006 16:55

9% at stock speeds, once you OC that difference at same OC speeds disappears :)

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