The Heatsink Guide: KryoTech Athlon-900

THE HEATSINK GUIDE: A look at the KryoTech Athlon-900

Temperature display of the KryoTech Athlon CPU

Introduction

The KryoTech vapor-phase cooled PCs were featured the most amazing PC cooling systems ever produced. Even though they never had a real commercial success, and are out of production for many years, it is nevertheless interesting to have a look at the technology behind these supercooled PCs.

The system

KryoTech's Athlon-900 came with the same case that was already used for earlier K6-based KryoTech systems, as well as the later KryoTech Renegade. It has three 5.25" and two 3.5" externally accessible drive bays. One additional cooling fan can be installed. The freon-based cooling system with its compressor is hidden in the lower part of the case.

The motherboard used was a MSI MS-6167 (Slot A, for first-generation Athlon CPUs). The case was very well designed, but due to the location of the "thermal bus", is was quite tricky to mount the fixation screws for PCI cards. KryoTech took great care to prevent EMF-related problems (which is especially important with high-frequency CPUs). Even the smalles holes in the case near the CPU were covered with copper tape, as you can see on this picture, so you're pretty safe from high-frequency electromagnetic waves. KryoTech also fixed a small fan inside the case, which blew air directly at the motherboard's voltage regulators (at that time, there were no motherboards equiped with fans for voltage regulators by the motherboard manufacturer).

What happens if you turn on a KryoTech system? Well, at first, the compressor will start, and cool down the CPU. During this process, the compressor runs at full power, and is quite audible. After 45 seconds, the CPU has reached the operating temperature, and the motherboard will be powered. From this moment on, KryoTech's Athlon 900 behaves like a normal PC, just as fast as later air-cooled and unoverclocked 900MHz Athlons. During normal operation, the compressor is not as noisy as before startup, and all you'll hear is the big 120mm NMB fan which provides airflow for the cooling system. All in all, the system was not very quiet, but not excessively loud either.

Preventing condensation

How does KryoTech handle the condensation problem? Many hobby overclockers who have experimented with peltier elements know that as soon as you cool your CPU below ambient temperature (and KryoTech cools way, way below ambient temperature), the main enemy is water condensation. How did KryoTech solve this problem? They used a combination of insulation and heaters. The CPU was located inside a sealed box, the so-called "KryoCavity". There were heaters inside the box, so that despite the -40°C inside, the outside of the KryoCavity would stay at ambient temperature. But of course, not the entire CPU can be inside the KryoCavity - the connectors must stick out, so that the CPU can be installed in the motherboard. This causes another problem - the metal leads on the CPU are of course thermally conductive, so without special precautions, the cold CPU would cool down the entire motherboard, and cause condensation problems there. To solve this problem, KryoTech used a heating wire, which keeps the CPU slot comfortably warm (around 30°C).
The thermal bus, where the liquid freon travels towards the CPU, and the freon gas travels back to the cooling system, also has a thick insulation. I also suppose there's a heating wire inside the thermal bus, but I couldn't verify this.

What happens if you turn the KryoTech system off? Due to the electrical heaters involved, electricity is needed to prevent condensation. This means that you can't just turn the system off by pulling out the power cord. The heaters must continue to heat the system, until the CPU has reached ambient temperature. So, after you've turned the system off, it must stay plugged in for a while. A few minutes after turning it off, the KryoTech system will emit a chirp, signaling that you can now unplug the power cord. This also means that in the case of a sudden power failure, the system is incapable to prevent condensation.

The KryoTech system shuts itself down automatically if the CPU "overheats" - that means, if it reaches a temperature of -29°C, due to a defect or due to excessively high ambient temperature.

Let's have a look at the inside of the system:

The components of the cooling system (Image in PNG format)

A safe investment?

Generally speaking, cooling systems are a safer investment than CPUs, since they can still be used after a CPU upgrade. However, in the case of the KryoTech Athlon-900, already its direct successor (the "SuperG" running at 1GHz) came with a stronger compressor, so upgrading the 900MHz unit to 1GHz wasn't possible. And only months later, AMD switched from Slot A to Socket A - which required an entirely new KryoCavity. So, for the few people who bought it, the KryoTech Athlon-900 was not necessarily a safe investment.

Some more pictures...

The KryoTech case, with the side plates removed.

The condenser of the KryoTech cooling system.
Here's where the heat of the CPU is actually transferred to the air...

View from behind. Notice the big fan in the lower part!
View from behind. Notice the big fan in the lower part

The reviewer
Look what a funny hairstyle I had, back in the time when an Athlon-900 was the fastes PC available