Atari ST Drive Swap

Introduction

This page describes how to add a drive swap switch to your Atari ST or STE. This switch will swap drives A & B so the external drive becomes drive A and the internal drive becomes drive B. The reasons why you would do that are:

Of course, doing this modification is totally on your own risk!

 

Parts required

 

Schematics + build description


Drive swap switch schematic.

 

The drives are selected by bit 1 & 2 of port A of the YM2149 soundchip. These are pin 20 & 19 on the soundchip. So by swapping these signals the external drive becomes drive A and the internal drive becomes drive B. The switching of the signals is done by a double-pole double-throw (DPDT) switch. Below is a step-by-step description of you to perform the modification. If the description is not clear, refer to the schematic above.

 

¹ If you don't want to cut the pins of the soundchip, it is also posssible to cut the two traces running from pin 20 & 19 on the motherboard and solder the wires at the proper places on the moterboard. But you need to be carefull to cut the traces at the right places. If you cut the traces too far from the chip it might be possible you swapped the signals to only one of the floppy connectors (internal & external) instead of both floppy connectors.