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Does anyone have a schematic over the Microdisc power supply? I missing mine and was thinking of making my own. My Microdisc uses a LM323 (which is positive) and the Oric uses a 7905 (which is negative), so I'm a little confused as to how they get a common ground.

Hello Igotafo

The oric and the microdisc use a independant transformer for each one (it is not a general power unit like PC) then in a "floating voltage" configuration you can connect these two devices without shortcut circuit problem. (the -5v Oric become 0v Microdisk)
The problem of the 7905 negative regulator is the impossibility to connect a transformer alone (single coil) for the both devices.

Then... The transformer inside of microdisc psu has three output windings? One for Oric computer, one for 5V microdisc and one for 12V microdisc?

I made a schematic for my PSU plans, see below. I'm not sure exactly what transformers I should use though. The Oric input wants 9V unregulated DC as the schematic says, I guess then U1 should be around 7V or something? I've never designed a PSU before

I'm using a 7.5V 1A psu to power my Atmos and it work fine and cold. I recommend use a 7.5V psu instead a 9V psu for 7905/7805 regulators.

Igotafro, I suggest to use a transformer with 7.5Vx2 1A or 1.5A windings to feed 7905 and LM323, and a 15V 1A transformer to feed to 7812.