This left one format conspicuous by its absence -- my trusty old BVU-870 U-Matic deck which was designed and built before the idea of S-Video (Y/C 3.58) output was conceived of. However, U-Matic machines did use a special 7-pin component output (officially Y/C 688 but generally just called "Dub") which was intended as a short cable, straight-through connection for tape duplication. And while the luminance (the high-detail B&W part of the video signal) is identical in output to modern S-Video, the chroma (the low-detail color part of the video signal) is encoded differently and is not S-Video compatible.
Now, years ago there were two companies who made gear that would transform dub output to S-Video but it was never made in large quantities and is now very hard to even find information about it. But while Googling I found a forum posting with a not-very-detailed account from someone with a different model unit than mine. He was able to attach wires to specific points on the circuit boards inside the unit and obtain a Chroma signal that was actually S-Video friendly. Since I have the service manuals and wiring schematics for my machine, I spent a night pouring over the diagrams until I found exactly which circuit boards I needed to study and some likely locations where I could "steal" the signal. My guesses turned out to be pretty shrewd because I was able to get a watchable signal the first time. It wasn't perfect, of course, and it took a few more tries to find the best points to tap the signal from, but suddenly I was getting video that was visibly better quality than anything I was used to seeing from the U-Matic format!
From there, it took me three trips to the local electronics shop to figure out what I actually needed to wire things up permanently, and I spent a night Googling just to find that special 7-pin connector so I could obtain the luminance signal from its proper location. Ultimately, I decided to use female BNC connectors so I could use my existing video cables to run the separate chroma and luminance signals to the rest of my gear. After a couple evenings with my soldering iron I'm proud to say I have something that looks pretty damn good and works a treat!
|Here's where I pull the color signal from the Chroma Decoder board's test points. Only after spending an hour trying to find the test points from the schematic did I realize the service manual also included a map of the circuit board.|
|The custom cable feeds out the back of the unit to this nice connector.||This takes just the luminance signal off the Dub Out port.|
To give you an idea of just how much of an improvement this makes, here are screenshots from the composite output (above) and the S-Video output (below) from the same segment of videotape. Note how much "cleaner" the color bars are!
And lastly, I've captured one frame of video using both sources and made a composite using a checkerboard pattern to show off the differences. I deliberately used a low-quality piece of video which has been copied several times from a very old (1973) source tape. This is why the S-Video output appears much grainer than the composite video. But even so, look at how much more detail is in the reporter's jacket!
Damn, I'm proud of this!