On Jul 9, 2011, at 11:54 AM, Chris M wrote: > > > --- On Sat, 7/9/11, Clark Martin <[email protected]> wrote: > >>> I recall seeing the mac video being designated a >> "composite" signal. >> >> Not even the Mac Plus is composite >> video. I've seen the connection to the >> analog board and there was, IIRC, video and both sync >> signals as separate lines. As a rule you don't use >> composite video for computers as it doesn't allow for a very >> crisp image. and the Plus has a crisp image. > > Generally this is correct. Composite-NTSC signals are "noisy" or whatever. > But I seem to recall many earlier color macs, if not most or all, pump sync > signals onto the green input. Now isn't that a composite signal? Maybe not as > convoluted as combining the entire video signal w/sync. And there may even be > some minor but mostly imperceptible degradation there too. It's just that are > different types of "composite" signals. If you've ever looked at a diagram of > an NTSC signal, w/the "back porch" and all other sorts of weirdness, you'd > likely get an indication of why assembling then disassembling the various > components results in something less then an ideal signal.
Sync on green is not Composite video. Composite video is a specific format for NTSC video with vertical, horizontal sync, luminance (intensity) and chrominance (color) signals all combined. Sync on Green has Red, Green and Blue signals all separate with the sync combined with the green signal. But the video signals are separate so it's not composite anyway. > Honestly it's been years since I've even looked inside a compact mac. The > analog board combines a power supply and circuitry needed for the crt and > whatnot. At what point are you saying the syncs and video are separate (or > separated)? Every composite monitor separates the signals at some point. The > composite signal is "understood" to parts of the monitor, but it's useless to > the nitty gritty (crt, flyback transformer, etc) until broken down. The sync and video are separate in the Plus, they are never combined. Take a look at: <http://home.earthlink.net/~gamba2/images/plus_analog.PDF> Page 10 shows the connection from the logic board. Clark Martin Redwood City, CA, USA Macintosh / Internet Consulting "I'm a designated driver on the Information Super Highway" -- ----- You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To leave this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/
