Macintosh SE Composite Video Signal

Thread Starter

Protochu

Joined Dec 14, 2019
5
Hello! first day here on the forums!
recently the display in my Macintosh SE broke (the pins came off from under the suction cup when I tried to remove it) and rather than try to find a new display (or repair a part the uses high voltage) I decided to have some fun and wire up a way to use an external monitor on the machine, however I'm having some trouble with generating a Composite video signal, you see i have 3 wires; Video, Hsync and Vsync. When I connect these wires to an RCA video plug and try to use a monitor, I get no output , why is that? Do I need to build a special circuit to properly make a Composite signal? If so how would I go about doing that? I would like to try to make the circuit as simple and as small as possible.

Here's what I've tried so far:
Video to RCA (no H/Vsync)
Video and H/Vsync to RCA

Some extra side notes
There is no video chip, its all done on the processor
Machine is from the 1980s
The wires come from the main board to a analog board that also charges a CRT
I sadly know very little about video signals

Thank you!
 

MrChips

Joined Oct 2, 2009
27,685
Welcome to AAC!
There are three important components in composite video.

1) Horizontal sync
2) Vertical sync
3) Video

You need to mix these three signals in the correct manner in order to create composite video.
Google composite video to learn how this is constructed.

To begin, you need to combine the HOR SYNC and VERT SYNC into one signal with the correct phase and polarity.
Next, you add the video signal to the SYNC signal.

You can view my blog and see how I generated and mixed the three signals to create composite video.

https://forum.allaboutcircuits.com/ubs/diy-pong-part-1-of-4-getting-started.822/
 

ronsimpson

Joined Oct 7, 2019
2,529
If I remember right; the horizontal frequency is 22khz which many modern monitor will not work with.
I remember the H. sync being about 50% which is not common, and many monitors will not work with.
...I believe I had to use a "one shot" IC to shorten up the H. sync pulse to make it more standard.
Vertical is 60hz which is very common.
...I think it is possible but finding the right monitor is not easy. Not VGA. Not CGA. Might work on a EGA monitor.
 

Thread Starter

Protochu

Joined Dec 14, 2019
5
Welcome to AAC!
There are three important components in composite video.

1) Horizontal sync
2) Vertical sync
3) Video

You need to mix these three signals in the correct manner in order to create composite video.
Google composite video to learn how this is constructed.

To begin, you need to combine the HOR SYNC and VERT SYNC into one signal with the correct phase and polarity.
Next, you add the video signal to the SYNC signal.

You can view my blog and see how I generated and mixed the three signals to create composite video.

https://forum.allaboutcircuits.com/ubs/diy-pong-part-1-of-4-getting-started.822/
Thank you i'll read up on that right away!
 

Thread Starter

Protochu

Joined Dec 14, 2019
5
If I remember right; the horizontal frequency is 22khz which many modern monitor will not work with.
I remember the H. sync being about 50% which is not common, and many monitors will not work with.
...I believe I had to use a "one shot" IC to shorten up the H. sync pulse to make it more standard.
Vertical is 60hz which is very common.
...I think it is possible but finding the right monitor is not easy. Not VGA. Not CGA. Might work on a EGA monitor.
after I i get the video signal i have an analog to digital converter so i can use HMDI
 

ronsimpson

Joined Oct 7, 2019
2,529
Found another box that supports these formats:
  • Supported Input Resolutions
  • 640 x 480
    • 800 x 600
    • 1024 x 768
    • 1280 x 720
    • 1280 x 1024
    • 1360 x 768
    • 1600 x 1200
    • 1920 x 1080
  • Output Resolution: 720p and 1080p
  • But does not support "TV" formats.
 
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