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Macintosh 12" RGB Display - Composite?
Posted by: markyb86 on 2012-10-27 04:06:58


Is there any way to run composite video to this screen?

Probably a dumb question (and actually pointless) but I was just curious and thought it might be cool to hook my digital tv converter box to in the dungeon.
Posted by: Trash80toHP_Mini on 2012-10-27 13:17:47
Gotta run it through a card in an LC or NuBus Mac that supports that resolution to get it up and running, AFAIK.

I don't think anything from the 630 on will drive it, bit if I'm wrong, that'd be your best bet.
Posted by: Byrd on 2012-10-27 18:42:11
Considering that Apple did make a composite output version of this 12" screen for Apple II/IIGS models, I'd crack it open to see if there is any way you could add a composite input. It might be a fairly easy mod to do.
Posted by: markyb86 on 2012-10-27 18:57:33
Hmm. I will crack it open on Monday and see what it's got in there. googled for about an hour today and what I came up with (as far as converting composite to analog rgb) was a bit out of my skill set as far as microchips and bread boarding. I can solder, but IC's are just not something I am familiar with.
Posted by: highlandcattle on 2012-10-28 02:05:57
Considering you can use it to display RGB computers like Amiga's or Atari ST's I guess it should be possible to hook up any RGB device. Considering that RGB gives a much better colour image then composite. You should try to hook up your device through there rgb ports. You will need to make custom cable though!
Posted by: Trash80toHP_Mini on 2012-10-28 06:25:00
Now that's a great notion for a hack, Component Video -> RGB would be very interesting.

One of my Mac cables is 5 BNC, so the signals should be available . . . no coffee yet so no research for a while . . .

. . . tapping into all the proper points on the controller board from an A/B switch just might work out.
Posted by: CelGen on 2012-10-29 09:39:29
The first thing you'll find is that the refresh rates are non-standard to NTSC.
Posted by: Trash80toHP_Mini on 2012-10-29 10:25:15
In that case, it's an interface card or nothing.
Posted by: Bunsen on 2012-10-29 11:35:26
Considering you can use it to display RGB computers like Amiga's or Atari ST's
[citation needed]

the refresh rates are non-standard to NTSC
[citation needed]

No, I'm not nit-picking - this is an area of interest to me and I would like to see documentation if possible 🙂

Component Video -> RGB
TV & Monitor Repair FAQ -> Notes On Video Conversion

I'll bet there's a link to a component-RGB converter schematic in there someplace. It shouldn't be too complex - as you say, all the signals are available.
Posted by: James1095 on 2012-10-29 11:40:36
There are IC's that will separate composite and component into RGB, that part is simple enough. Very few RGB computer monitors scan anywhere near the 15.7 kHz horizontal of NTSC though, most are close to double that or higher. Displaying NTSC on one of those requires a scan converter, it digitizes two interlaced fields into a frame in a RAM buffer and then converts that back to a single non-interlaced frame at the scan rate supported by the monitor. It's possible to do, but certainly not worth the effort unless you have a very specific need.
Posted by: James1095 on 2012-10-29 11:43:45
I found specs for the M1299 RGB monitor in about 10 seconds with a search engine.

http://www.monitorworld.com/Monitors/apple/12colordisplaym1299.html

Fixed frequency, 512 x 384, horizontal 24.48 Khz, not even close to NTSC.
Posted by: James1095 on 2012-10-29 12:02:32
For those who are curious, here's an excellent example of what is involved in doing this.

http://elm-chan.org/works/sc/report.html

This circuit could be modified to work on a 24 kHz monitor if one was inclined to do so, but it's quite a lot of work. Mr. Chan's creations are very impressive, all hand assembled on perfboard, but it would have been FAR easier to duplicate if he had used a PCB layout instead.
Posted by: olePigeon on 2012-10-30 13:49:11
Hah. I just noticed that itty bitty 3" (?) screen next to the monitor. 😀 That's funny.
Posted by: CelGen on 2012-10-30 14:22:10
[citation needed]
NTSC video is broadcast and displayed at 640x480 with a refresh rate of 60hz. On the Macintosh the original....

http://support.apple.com/kb/SP421

Ignore me. I was thinking of that dumb 66.7hz refresh rate they used. xx(

Posted by: markyb86 on 2012-10-30 14:36:10
That little guy would be nice to have haha
Posted by: markyb86 on 2012-10-30 14:37:26
For those who are curious, here's an excellent example of what is involved in doing this.
http://elm-chan.org/works/sc/report.html

This circuit could be modified to work on a 24 kHz monitor if one was inclined to do so, but it's quite a lot of work. Mr. Chan's creations are very impressive, all hand assembled on perfboard, but it would have been FAR easier to duplicate if he had used a PCB layout instead.
You aren't kidding about that being alot of work
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