Cooling the A4000 desktop version

The original desktop case for the A4000 is notorious for overheating - especially if the A4000 has been expanded a lot. Listed below is a series of hints for improving airflow through the A4000. As a bonus the A4000 will also be quieter.


Some of these modifications involve modifying the power supply which contains LETHAL voltages. Make sure you remove the mains power cord before attempting any of this work. Do not attempt modifying the power supply unless you really know what you are doing. You may damage the power supply, causing electrocution or a fire next time it is powered up. If in doubt get a qualified electronics technician to do the work. I will not accept responsibility for any damage or injury caused by these modifications. Perform them at your own risk.

The diagram above outlines the main airflow path through the A4000. It enters through the perforated frame around the Zorro backplane, passes over the Zorro expansion cards, then through the gap between the Zorro daughterboard and the front panel. The airflow continues over the CPU board, then enters the power supply through the fan and is finally expelled through the louvres at the back of the power supply.

In order to improve airflow, the work has been broken up into sections. They are numbered orange in a square box in the drawing above. Doing the work on each section will provide an incremental improvement.

Section 1:

This is where the air enters the A4000. It is a perforated frame around the Zorro backplane. First, make sure it is not clogged with dust. Clean it with a soft brush. Airflow here can be improved by cutting away the section above the top Zorro slot. This will be hidden when the A4000 cover is fitted. If you have a Zorro card that needs extra cooling, you can then place it in the top slot, as there now will be more airflow along the top board. Another way to improve airflow is to remove some of the blanking plates in unused slots.

Section 2:

Firstly, read and understand the caution above. This section deals with the fan, which is located inside the power supply. Airflow can be improved by cutting away the perforated area in the case of the power supply in front of the fan. It can be left open, though make sure cables don't get lodged in it, or you can fit a wire fan guard to cover the opening. These guards can be found at electronics stores, or out of the power supply from an old PC. As a bonus, the reduction in air resistance will also make the fan quieter. Incidentally, try to route the ribbon cables for the drives in a way that allows free airflow in the area in front of the power supply.

The fan itself can be sped up to provide more airflow. To do this, the PCB needs to be removed from the power supply case, and a 47 ohm resistor in series with the red fan lead shorted out. This will then mean that the fan will be running on its full rated 12 V DC, and will be faster (and noiser - though this is more than offset by cutting away the perforations). The resistor is located on the PCB itself, next to the fan lead.

Section 3:

This is where the warmed air is expelled out the back, through a set of louvres stamped in the case of the power supply. Again, read the warning above. These louvres restrict the airflow. There are two ways to improve it - a screwdriver can be inserted (with the power off!) and the louvres bent to widen the gaps. A better way is to actually cut away the louvres, and fit a metal fan guard over the hole. Do not leave the hole exposed as there will be high voltage components exposed. Don't forget to remove any metal filings left over before powering up!

Section 4:

This section is optional, and is intended mainly for those with CPU boards that generate a lot of heat. Cut a hole in the metal panel and fit a small CPU fan over the hole, with the airflow blowing across the CPU board. Since the air comes from the gap between the plastic front panel and the metal case, you may need to drill a couple of holes in an unobtrusive spot in the plastic panel to allow airflow.

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Introduced December 20th 1998. Revised December 20th 1998. Version 1.0