there is two sets of diodes on the original board set and a big white resistor near the bottom corner. One set of diodes is for the audio amp and they are the ones closer to the amp. The ones for the +5 is farther away. If I remember right the +5 ones go to a resistor and regulator.
I use a switcher supply and solder a computer drive connector to the board. I solder the yellow wire to the output (cathode) of the diodes near the audio amp and supply +12 there. I put the +5 red wire to the other set of diodes at the cathode. Now since I don't like to put much more than +5 to my board, I jumper the big white resistor at the lower right corner of the board when edge connector to the left. That resistor will drop the voltage so some just leave it alone and bump up the switcher to about 6 volts.