Modifying a CoCo3 to run on 12VDC
Running a CoCo 3 from 12 volts DC is actually a very easy modification, and easily reversible.
The first step is planning and procuring all the materials you will need. You will need a suitable DC power supply and socket to connect it. You will need a jumper wire about 1-1.25 inches long, solder and soldering iron. I also used a small round file and hot-melt glue gun. Individual needs may vary.
The CoCo3 with floppy controller and 3.5" drive draws about an amp, not including the video display.
Choose a power socket that suits the power supply you are using. I chose one that fit both a 12VDC 1Amp wall-wart (transformer) and a vehicle lighter socket cord I had handy.
I drilled out the center strain-relief pillar and used a round file to make the hole large enough to accomodate the power plug. The socket is held in place with hot-melt glue.
Installing the socket is actually the hard part. Modifying the CoCo3 requires removal of the transformer and power cord, and the addition a single jumper to bypass capacitor C62.
The schematic below shows that normally C62 provides filtering of the half-wave AC power being fed to the RF modulator and audio circuitry. Since we are providing DC, and a capacitor in series blocks DC, we must route the power around it, otherwise we get no sound or RF output.
That's all there is to it.
Bob