Designing a C64 RF Modulator Replacement Phase 1, Part 2

Drawing a New Schematic

In Part 1 of this particular hair-brained scheme, I decided to design and build (or at least try to), a new RF Modulator replacement for my 250466 SixtyClone board.

I broke the project down into Phases and illustrated the 5 different areas that were clearly defined by the original schematic. I finished Part 1 by outlining the three parts of that schematic we need, and the two that we don't.

I must also remind you this is NOT a tutorial. I have no training in this stuff and am in no way qualified. All I am doing here is seeing what I can manage to build and bringing you along for the ride.

With that recap out of the way, we can move on.

There is one area of the Schematic I have ignored until now, but without it, we're going nowhere.

I've stated very clearly above my amateur credentials here and know full well that anyone with more advanced knowledge than my own will be face-palming at my stupendous ignorance, but that's ok, I'm not passing my blundering off as a tutorial.

So, yeah, the bit that I ignored till now is Ground. Would it shock you to know I don't actually know what that is? I can quote pages of explanations that I've Googled and the best explanation I've come up with is that Ground is simply a reference point carrying 0 volts. I know what those words mean but have no clue what the implications of that are in any practical sense. Electronics is hard. I'm not certain I actually need an in depth understanding, however: I can see with my eyeballs that the original schematic shows it, and I know I need to include it for the circuit to work.

So lets highlight Ground in our original schematic:

Doing this, we can see clearly how ground is attached to each of the five circuits. We need to preserve the parts of this we need, but remove the parts we don't.

Let's now just delete the Audio and RF Circuits from the schematic:

We can see the ground connection is just hanging as we've deleted all the wires that used to exist. We can also see that the power circuit at the bottom is no longer connected to the rest of the circuit. Before we deal with that, there's a part of the Luma circuit that is now orphaned (i.e. not connected to anything), highlighted here in red:

Now, like all of this, I'm simply guessing, but it seems to me we can remove this as it simply seems to have been feeding the luma and color signal to the now removed RF Circuit. Let's delete that and tidy the schematic up a bit by joining up the bits that need to be connected:

Much better, but I can now see another part of the schematic that appears to be orphaned, again highlighted in red:

As far as I can see, this part was only needed to feed power to the now removed Audio Circuit. so I will delete that, and tidy up the ground wire:

Now it's by no means certain, but I think this is a workable schematic. All I've done, literally, is a bit of cutting and pasting but this seems to make sense. We will find out soon enough just how janky this is, but with what I'm calling Revision A now in the can, it's time to embark on the laborious task of identifying and sourcing the components. Read all about that in Phase 1, Part 3.