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Jaguar RGB cable—any difference between different video ground pins?


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#1 electronizer OFFLINE  

electronizer

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Posted Fri Dec 7, 2018 6:19 PM

I'm building a Jaguar A/V connector to VGA (HD15) adapter that I can use with my standard VGA to RGBHV cable. I have a display capable of accepting composite sync so I'm planning to use the series 220uF + 680ohm resistor attenuation I've seen elsewhere on the TTL CSYNC output. For quick building, I'm using an IDC edge connector and a short piece of ribbon cable along with an HD15 plug with crimp connectors.

 

It's easiest to build this cable if I have separate ground wires coming off the ribbon cable for the video and sync ground connections. Pin 10 in my RGBHV cable is connected to sync ground for both Hsync and Vsync, and all of the RGB grounds in the cable are connected together, so really I just need two ground connections from the Jaguar.

 

I notice in the Jaguar schematic that there are four video grounds: 4A, 3B, 7B, and 10B. So, I could hook one of these to sync ground, and one of them to any one of the R/G/B grounds in the HD15 connector. I have two questions:

 

 

-The schematic shows a ferrite bead inductor on video ground 3B. Is there any advantage to using this ground over the other video ground connections, which don't have a ferrite bead?

 

 

-Is there any reason to connect all three RGB return pins as well as pin 5 in the HD connector to ground? (The VGA specification says pin 5 is Hsync ground, so e.g. would making these connections allow me to use a standard VGA cable to display an image with CSYNC connected in place of vertical sync?)



#2 Zerosquare OFFLINE  

Zerosquare

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Posted Sat Dec 8, 2018 1:37 PM

-The schematic shows a ferrite bead inductor on video ground 3B. Is there any advantage to using this ground over the other video ground connections, which don't have a ferrite bead?

It doesn't look so. The official SCART cable uses it as a ground for the red channel. In fact, it simply pairs each signal with the closest video ground on the connector.

-Is there any reason to connect all three RGB return pins as well as pin 5 in the HD connector to ground? (The VGA specification says pin 5 is Hsync ground, so e.g. would making these connections allow me to use a standard VGA cable to display an image with CSYNC connected in place of vertical sync?)

Connecting more grounds won't hurt anything and can help reduce interference between signals, so I advise doing it.
A good-quality VGA cable will work well, since it has the correct impedance and good high-frequency specs. Just keep the ribbon part short.
Note that whatever monitor/converter you're using must support composite sync and 15 kHz signals for it to work. Most VGA monitors don't.
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#3 electronizer OFFLINE  

electronizer

    Chopper Commander

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Posted Mon Dec 10, 2018 12:31 AM

Thanks for the input Zerosquare! I ended up using 3B for sync ground and the other three grounds for the RGB returns. The result is night and day compared to the RF out. Nice, clear picture. I have the output connected to a DVDO iScan HD and from there to my LCD TV.

Here is what the cable looks like:

981207EE-FC4C-4405-8179-BDE25142A1E8.jpeg

Next I will have to try making an S-video and composite cable.




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