16-Oct-99 - Les shared his experience watercooling a K6-2/450
Hi guys,
Though I'd tell you about my system. The actuall CPU I have at the moment is a AMD K6-2/450 (2.4v core). The motherboard is an ASUS P5A-B. All temperatures I quote were measureed at the centre bottom of the cpu with thermal paste between then sensor and the cpu. This gives me fairly accuarate ans dynamic temperature readings.
This particular cpu was a pig to overclock. My first attemps to get it running at 500 were hopeless. If I raised the core voltage to 2.5 or more the core temp would exceed 80 deg if I saturated the cpu (100% load). It would consequently crash, but at any voltage less than this I cannot even get post. I was already using a very large heatsink and 100mm cooling fan (thats not a typo). First I added a copper heat spreader to the heatsink and ground the cpu top flat (as well as the heatsink). Under full load I had droped the core approx. 10 deg. Still not enough. I had through much experimentation discovered almost exactly the temp the cpu would start to misbehave, roughly 57 deg c. I had achieved 70 :(.
Back to the drawing board. I wasn't game to lift the core volts any further because of the high temps I was seeing, and previous attemps with peltiers always caused my condensation problems (although I intend to add peltiers to my current design). So I needed more cooling. At this point I decided water would be the way to go. I ended up with a 50mmx50mmx22mm solid copper block with 36 x 2mm hole through it with chambers at both ends and 8mm copper inlet and exhaust tubes.
I pump this with a small 400 litre/hr submersible pond pump (nice and quiet because its submersed). This pump is suspended in a 2 gallon plastic bucket .
It pumps water directly from this reseviour to the heatsink (which attaches to the socket 7 just like a conventional heatsink but with a custom made clip of course). The return line from the heatsink passes through a Holden transmission cooler which is oriented horizontally (I always let convection aid me) and has a 240V 6" fan attached to the top and exhausting upwards (again to aid convection rather than fight it).
With this setup I pulled another 20 deg out of the core. Suddenly 500 almost became stable. With this lower core temp I started to lift the vcore a little more. At 2.7 I finally achieved stable 500mhz operation. Time to start ramping up the front bus. My 500 was at 5 x 100 of course. Next I went for 4.5 x 115mhz. (I'm using 128mb generic pc100 sdram with bios settings set to 143 mhz ram setup). This was fairly stable for several hours but not completely. I upped the vcore to 2.85v (I modified the vcore regulator with a 10 turn pot so I have more precise vcore control). At this voltage The computer is completely stable (3d games and Mac emulator running for 48 hrs no crashes). My actual cpu power consumption is almost 100 watts (yikes). When the ambient temp is less than 20 deg I can run all day at 4.5 x 120 (540mhz). My Guillemot PCI banshee card is also overclocked to 117mhz ram speed and 120 mhz core, again with the adition of lots of fans and heatsinks. In addition, I have fitted 2 x 4" fans in the front of the large server case I am using, and an additonal 3" exhaust fan at the rear.
I wouldn't ever recommend this vcore to anyone whatsoever of course. Without very carefull monitoring of the core temp, the voltages I am using would destroy the cpu in a very short period I would think.(When K6-2/450 are $10 I will probably see how long one lasts with only a conventional heatsink for cooling). It has been running this core voltage for about 3 1/2 months now. Hope you find this little info on my machine interesting.
CYA
Les Tutt
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