To use broadATX:

Ensure you have cleaned the board thoroughly and replaced the capacitors, or otherwise have had this routine maintenance performed. Supplying power to a board with active electrolytic leakage can rapidly worsen any present damage.

Installation

Open your Macintosh II series computer and remove any Nubus cards present.

Disconnect the 15 pin power connector, and remove the existing power supply (if present).

Rotate and align broadATX to mate with the 15 pin connector on your Mac II. The ATX connector should be on top with its locking tab towards the motherboard.

Carefully and consistently press the connector into place. This can be a challenging negotiation, but all pins should be inserted at their full depth.

You may now reinsert and arrange your Nubus cards. Note that slots A and B will only accommodate  7" Half Length cards due to the space occupied by broadATX. All other slots will allow 12" Full Length cards.

While disconnected from mains power, plug the ATX power supply of your choosing to the 24 pin header. If you are using a 20 pin ATX connector, simply move the connector two pins over. It will not engage the locking tab, but will function normally.

Placement of the ATX supply is left as an exercise for the reader, but these machines provide more than enough sheer cubic volume for experimentation. Alternatively, if available, a TFX form factor power supply reportedly fits very neatly into these machines.

Starting up

Attempt to power your logic board by either using the soft power key on the keyboard or the rear power switch. If neither of these options result in a successful boot, the Force header can be used. By default, this is shipped in the inactive position. To use it, simply remove the black jumper from its current position, then place it one pin to the right, towards the 'E' in 'FORCE'. If this still does not result in a successful boot, there is likely a deeper issue at play.

Shutting down

If your machine works without the use of the Force header, this action should be indistinguishable from normal behavior. Shutdown via the Mac OS menu should behave normally.

If you are making use of the Force header and attempt to Shut down from the title bar in Mac OS, your Mac will idle indefinitely at the 'It is now safe to turn off your Macintosh' screen (A vestige of the compact Mac's ROM). This is expected. Your Mac is in a shutdown-ready state and the disks are parked, but your machine will require your intervention to actually disconnect power. You should only ever disconnect the ATX supply from mains power in this scenario, never the 20 or 24 pin connector from broadATX. Alternatively, a future product offering will allow an empty Nubus slot to be used as a switch for the force header.