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AMD K6-3 Overlocking Hints

(02/21/00)

WHO? This document is written for the owners of AMD K6-3 processors who wish to overclock their processors. You should already be familiar with typical overclocking procedures. If you feel uncomfortable opening your case, this page is not for you. The steps describe below can potentially permanently destroy your CPU. You should not attempt any of the suggestions here unless you are willing to risk destroying your CPU.

WHAT? This page contains my overclocking experience with a 2.2 volt AMD K6-3 400MHz processor (CTX core).

WHY? Presumably, you should already know why. I have not owned a CPU that I haven't overclocked. The very first processor that I tried to overclock was a 486 DX2 66MHz processor that ran at 80MHz. I've since overclocked a Pentium classic 75MHz to 133MHz, Pentium 200MMX to 262MHz. Currently, my dual Celeron 400MHz processors are running at 600MHz!
There was a huge debate then about how electromigration may damage overclocked processors. Of course, even if electromigration is more prone to develop with overclocked processors, it's generally agreed that the process will likely take years. Either way, I have long sold the CPUs in question. 

HOW? Well, the AMD K6-3 processors don't seem to overclock nearly as well as the Celeron processors. Still, 50-100MHz is still better than nothing. The particular K6-3 that I have is a 400AFR 9944EPGW. The 400 denotes the rated CPU speed. AFR denotes a 321-pin CPGA 2.2 volt chip rated to operated between 0 and 70 degrees Celsius. The 9944 denotes 1999, week 44. Information on what the best weeks for overclocking are sketchy, and I don't know what they are. Linux reports this as a family 5, model 9, stepping 1 CPU. The following table is a compilation of data gathered from the AMD-K6®-III Processor Data Sheet.

AMD K6-III Processor Markings
A

Package type: 321-pin CPGA (Ceramic Pin Grid Array)

 
Operating Core Voltage
Power Dissipation (400MHz)
Power Dissipation (450MHz)
F
2.1V-2.3V (2.2 typical)
Typical: 10.85 W
Max: 18.10 W
Typical: 12.15 W
Max: 20.20 W
H
2.3V-2.5V (2.4 typical)
Typical: 16.10 W
Max: 20.80 W
Typical: 17.70 W
Max: 29.50 W
 
Case Temperature
 
-
R
0°C-70°C
 
-
X
0°C-65°C
 
-

The K6's are NOT multiplier locked, so if you cannot overclock the bus, you can manipulate the multipliers. The valid multipliers on a CTX core are 2.5x to 6x in .5 steps. The 1.5x and 2x multipliers are treated as 3.5x and 6x respectively. You can actually use this CPU with a variety of bus speeds. You DO NOT need a motherboard that supports the 100MHz bus speed or a special version of a K6-3 66MHz chip. Note: There aren't separate versions of the K6-3 processors! For example, the K6-3 400 is intended to run at 66x6 or 100x4.

My spare system was an Asus P55T2P4 w/ a Pentium 200MMX overclocked at 262MHz. When the price for a K6-3 CPU dropped to $76, I decided to upgrade. I have never bought a CPUs over $100. The highest working bus speed that the P55T2P4 can supply is 83MHz. Therefore, the highest theoretical speed is 500MHz on my P55T2P4. It's currently running rock solid at 450MHz@2.2 volts with no special cooling. It will actually POST at 500MHz, but my motherboard doesn't seem to like the 83MHz bus speed. I tried running 83x3.5 (291) with the same result. 

So, without further ado, here is how I got the K6-3 400 to reliably run at 450MHz (75x6) on my system. When I initially tried to overclock the chip to 450MHz, it was unstable at the rated 2.2 volts. The first trick that I tried was running it at 2.3 or 2.4 volts. Both setups appeared to be stable. Linux would boot. I can compile the kernel without signal 11 errors. However, after running SETI@home i386 client for a couple of hours, it would produce a segmentation fault (basically the same thing as a signal 11 error). This was obviously unacceptable. I didn't want to try a higher voltage, but I've seen reports where people were running at 2.8 volts! Note: Some of those reports could be results on the 2.4 volt rated chip. I can't tell you anything about the 2.4 volt type unless you're willing to donate it to me. =) I've briefly gone as high as 2.5 volts myself, but I wouldn't recommend going higher than that unless you REALLY know what you're doing. 

The next obvious thing to do is to improve the cooling. Since this is a budget setup, I didn't want to buy any new equipment such as a bigger heatsink or peltier. Besides, I don't really consider peltier cooling to be a good solution. You might as well buy a faster CPU. I had read somewhere that people were reporting higher overclocking success after prying the metal plate off the CPU and attaching the heatsink directly to the core. Since it wouldn't cost me anything but time, this is what I decided to try. WARNING: This can easily DESTROY your CPU if you're not careful, and can potentially happen even if you are careful! DO NOT TRY THIS unless you're willing to risk destroying your CPU! If your system is already stable, you should probably leave well enough alone.


As you can see from the inside of the metal plate, it is attached to the K6-3 at the four corners and the core by glue.

  1. Before you start prying, find something to protect the pins of the CPU. Don't come crying to me if you break a pin. I was lucky enough to find a CPU holder. You can try prying the metal plate off while the CPU is sitting in the socket of your motherboard.
  2. If you examine the CPU carefully, you'll notice that there is a slight gap between the CPU and the metal plate. The trick is to find a flathead screwdriver small enough to fit in the gap.
  3. Use an Exacto knife to score the glue slightly. Carefully pry one corner at a time.
  4. Once you're done prying all four corners, you can easily get the metal plate off by lifting from a corner. DO NOT pry anywhere near the core!
  5. You can carefully scrape the glue off the core with an Exacto knife. If you're not coordinated, get someone to help you.
  6. Apply a thin layer to heatsink compound over the core and reinsert it into your system.
  7. If you don't already have a front case fan, you should consider it as it will help you lower your case temperature and overall stability.
 


This is the bare CPU underneath. It looks surprisingly like a PIII FC-PGA.


After this removing the metal cover and attaching the heatsink directly to the core, my system is now rock solid running 450MHz@2.3 volts. SETI is now able to run for days on end without producing a segmentation fault. *UPDATE: After burning-in the K6-3 400 running the SETI@home client for several days, it is now running 450MHz@2.2 volts stable with just the heatsink (no fan).


 11:14pm  up 26 days, 23:31,  2 users,  load average: 0.99, 0.97, 0.91
25 processes: 22 sleeping, 3 running, 0 zombie, 0 stopped
CPU states:  0.0% user,  0.3% system, 99.6% nice,  0.0% idle
 
Shane Tzen © 2010
 
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