Overclocking the DKB Cobra

The DKB Cobra is a 68030 accelerator designed for use in the A1200. It was made in a number of different speeds. The one I had tried was originally at 28MHz, and belongs to an Amiga User Group which I am involved with.

When I first looked at the Cobra, I found to my surprise it was already overclocked. It contained a 20MHz 68030 running at 28MHz. After experimentation, I found I was able to get reliable operation at up to 44.9 MHz. At this speed, the 030 MUST be cooled, so I glued a heatsink to it. I then cut a square hole in the trapdoor cover to allow the heatsink to protrude underneath. Finally I attached a set of self-adhesive rubber feet to raise the A1200 slightly to improve airflow. This system has worked reliably for several months now.

During my tests, I had fitted an IC socket for the oscillator, and I found that this caused clearance problems with the A1200's case. This could either be solved by cutting away the offending part of the case, or by not using a socket. Bear in mind that your particular unit may not operate reliably at 44.9MHz due to different component tolerances, and so you may need to change the oscillator. Obviously this is harder without a socket. Another trap I discovered was that the oscillator pins had been bent over before soldering. This made it harder to unsolder and remove the existing oscillator. In fact I damaged one of the solder pads on the PCB and had to repair it to get the unit going. So, take extreme care when you are working on it.

A 68882 FPU rated at 33MHz had also been fitted to this particular board. The 68882 was also found to work reliably at 44.9MHz, so the board was set up to clock both CPU the one oscillator. Refer to your instruction manual to do this. The 44.9MHz oscillator was pinched from an old ISA VGA card from a PC.

Points to watch

* Take care when removing the original oscillator - the PCB tracks are fragile.

* Use a socket for the oscillator (you will have to hack the A1200 case for it to fit, however).

* Use a heatsink on the 030 and cut a hole for it in the trapdoor.

* Watch your power consumption - the A1200 uses a puny power supply, and overclocking causes a small increase in power consumption.

Back to main Amiga page.

Introduced December 20th 1998. Updated Feb 5th 1999. Version 1.1