After several weeks of head scratching, I can now power up my U.S. model IBM PC 5150, after converting its power supply from 115V input to 230V. Full details here.
If you like me you find yourself wanting an AT2XT adapter, you may have also discovered that they are not too easy to buy pre-made.
Here is one I built on prototype board, using an AT to PS/2 Keyboard cable:
Without the IC Socket on it, it looks like this:
Once the IC Socket is fitted, the tails from the AT to PS/2 Keyboard can be attached like so:
Here is the underside:
The last thing to do is wrap it in heatshrink tube:
A modified and compiled version for PIC12F675 can be downloaded here. I just fired it in with my Universal programmer, plugged it in and it worked perfectly first go.
If yours is using a PIC12F629 like the original design, get the firmware from the original project information page.