Free CTK-480 Keyboard
Got cheap keyboard from neighbors.
CTK-480 service Manual
Found service manual online while looking for user's manual.
P25/TXD "Not Used."
Service manual states tx on the processor is unused. We'll see about that.
There it is right below the clock circuit.
It even has a nice solder blob on the pad there.
Can it really be this easy?

Soldered TX to TX (It looks like there is a buffer after TX on the midi board), 5v to 5v, ground to ground, plugged in, and hey, the light flashes (YAY!) but software doesn't do anything. I guess it couldn't be that easy.

Looks like the CTK-481 has midi out. That is just one number bigger. Maybe it is using the same circuitry?

CTK-481 Service Manual
I'm loving that they all have service manuals floating around the internet.
Different processor, same family?
CTK-481 Schematic
Looks like it gets inverted.

I guess I'll probably need to invert the signal.

Mess of wires.
The values don't match the CTK-481, and I didn't put in the capacitor shown in the CTK-481 diagram... maybe it will work?
It's working!
It's working!