Changes
IMPORTANT – READ CAREFULLY! If you choose to mount the circuit in a similar manner as I have, using the 7812 heatsink, it should NOT be fixed directly to the MP1 aluminium heatsink! It must be electrically insulated, by using an insulator between the 7812 and the heatsink and a plastic screw/nut, or similar insulating setup. The reason for this is that the 7812/7805 heatsink is internally connected to pin 2. In our circuit, this is connected directly to ground, as is usually the standard. However, as you can see in the MP1 power circuit diagram above, the MP1 5V circuit has two resistors placed between pin 2 and ground (to slightly raise the voltage above 5V), meaning that the heatsink is not as normally expected at 0V, but is actually floating slightly above 0V at around 0.2V. If the 7812 was connected directly to the heatsink it would effectively short-circuit these resistors and mess up the 5V supply. I used a small piece of PCB with a 3mm hole between the 7812 and the heatsink, with a plastic isolating washer. The 7812 is only running at most at around 30% of its maximum capacity, so it shouldn't ever actually heat up and no heatsink is really required in this case. When all has been mounted and connected, the casing can be re-assembled and tested. Always test the voltage and polarity of the new socket BEFORE you test it with your CPC.
As we have all learnt from Hollywood Films, even psychopathic bomb-building maniacs seem to stringently follow the standard electrical colour codes (how else would Bruce Willis know that the blue wire is the one that de-fuses the bomb). Although it is not compulsory, I would advise you to use black leads for the ground connections and red for positive connections. It makes it a lot easier to recognise where to connect them without having to check back to the circuit again, and helps to avoid polarity mistakes, that could cost you your treasured CPC. On the 12V output socket, the positive should be connected to the outer ring and the ground to the centre pin.
