MC-10 composite

I bought a few TRS-80 MC-10 Color Computers to see what I could develop
for this machine. The first thing I decided it needed was something better than
the RF modulator output for video and sound that these machines come with.

So I developed this RF Modulator replacement that allows for composite video
and sound through the same jack. The jack is positioned where the RF jack
used to be on the computer, so there’s no need for case modifications.

The RF Modulator in the MC-10 generates the system clock, as well as
converting the MC6847 output into channel 3-4 RF. My composite board
generates the system clock, converts the MC6847 output into baseband
composite, and makes it (along with sound), available at a mini-headphone
style jack at the rear of the machine.

I decided to go with mostly SMT parts on this board (all except the
output jack and MC1372) as I’m getting pretty used to them now, and
after a while they aren’t any more work to assemble than through-hole
components, maybe less in some cases.

All the necessary signals and power connections are made through the
original connections for the RF box. The 6 and 3-pin headers at the front
of the board, and the grounding lug at the back.

Here is a picture of the board installed on an MC-10 motherboard.
Physical fit is excellent as a drop-in replacement once the RF box is removed.

MC-10 Composite REV 02
No Case Mod
View of output jack

Video output from this board is great.  Very clear, and about as good as can be hoped for from the MC6847/MC1372 combination.  Here are a couple of pics of the output.

MC-10 Composite output

As you can see from the pic below, the video waveform looks great!

NTSC video waveform showing one line of video

Anyway, the boards look pretty good.  I’ll use the prototype for a while, and if I continue to be satisfied with how it works, I’ll produce a run of these so other MC-10 owners can get some decent video output too.

Update 11/08/2015 I’ve had production PCBs made and now have some of these available for MC-10 owners.  No more noisy RF!  🙂

Final production version (hand assembled)

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