Connecting a C64c Board to PC Case Supply

    Powering a C64 computer with external +5V, +12V DC supply should not confuse anybody. At first glance, we can think that C64 cannot work without an AC 9V. If we think why AC and why 9V is needed we can find that it is not needed in reality ;-). C64 uses AC to extract 50-60Hz. tick for TOD clocks only. VIC doesn't require it to time the composite video picture. Also AC nature of 9V is used to convert this 9V to 12V with a simple coil/transformer. This 12V, after conversion to DC, is used for powering SID. And C64 can do without a SID chip also. This 12V DC or 9V AC (depends on the version) is also connected to the user port. Thus, if we know where to connect a +5V DC and GND to C64 we can make it work. But if the sound is needed, we have to know where to connect the +12V DC either.

    The correct location to connect +5V and GND, can be found even by a short look to the C64c PCB. GND occupies large areas on board generally, especially near the power connector. I chose one of the gnd legs of this connector to solder the ground level wire. And +5V is the second after GND which occupies large trace areas. But we need a very first entry to the +5V trace. So, we again look for a place near the power connector. Actually there is a good place to solder our +5V wire. It's one of the legs of R19 resistor, which is connected directly to the power switch. But, we have to remember that the switch must be off always for this connection, otherwise a short-circuit happens to the power supply. Lastly, the +12V wire has to be connected. We need a place after the regulator circuitry, to connect this wire. And the best place to solder this wire, as shown in the figure_1, is the positive leg of 1000 microfarad rectifier capacitor C63.

Actually, if you want you can run your C64 with 8 AA type batteries. Batteries must be grouped by 4, and these two groups must be connected parallel to a +5 regulator chip. Then the output of the chip must be connected to the C64c PCB as described above. There is enough room to put 8 AA size 1.2V rechargable batteries in the standard C64c case. To charge these batteries you need a 9V 100mA source and 10-12 hours. Of course, you cannot get sound with this battery solution. Instead of the AA size batteries you can use a car battery with a proper +5V regulator also.

    For Tower-C64 Project, we need to connect our power wires (+5V, +12V, and gnd) to the correct pins of a PC power supply cord. You can find the appearance of one of these power cords in figure_2. These cords have standard color codes for voltage levels. There are four wires: Yellow wire contains +12V DC, red wire contains +5V DC and black wires are corresponding ground levels.
After making these connections, your C64 will work if you press the power switch of tower case. And of course, watching a C64c running in a tower case is rather nice feeling.

March 1998
Ilker Ficicilar
filker@newton.physics.metu.edu.tr

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