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Slight Interference with Atari 2600 S-video mod when run through a switcher to Commodore 1702 Monitor

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I have an Atari 800, Commodore 64 and Atari 2600 all running through a 4 port Composite switch.



The output of the 4 port switch connects to the back of the Commodore 1702 Chroma/Luma inputs. (I did not know it but these standard composite cables carry the Chroma / Luma signals just fine).

Unfortunately the Atari 2600 suffers some slight interference though. I have the Atari 2600 s-video mod with an s-video to composite cable. When I plug that directly into the back of the 1702 the picture is perfect. When I run it through the switcher I get interference. I have tried many combinations but nothing seems to work unless the Atari is connected directly to the back of the 1702.


Here is my idea. I am thinking that I need to get all signals s-video directly to the 1702 or find a better switch. What if I get something like this: https://www.amazon.com/RCA-CRF940-Modulator-Gold-Plated-Connectors/dp/B00008X5DD/ref=cm_cr_arp_d_product_top?ie=UTF8#customerReviews


Here is the back picture:


Then I just run an s-video cable from the Atari 2600 into Input one. Run Atari 800 and Commodore 64 s-video cables into Input 2 and Input 3.

The output would just be an s-video to composite that would go into the Chroma and Luma on the back of the Commodore 1702 monitor.

Would this type of thing potentially eliminate the interference for the 2600?



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On 7/12/2020 at 3:56 AM, donjn said:

When I run it through the switcher I get interference.

I have a different 4-way switcher but it also screws with my S-video signals. I took it a part a couple weeks ago and discovered that the manufacturer had bridged the chroma luma lines from the S-video inputs with a couple filter caps and an inductor and basically down-scaled the S-video inputs into very bad composite outputs. But in so doing, this caused terrible interference on the S-video outputs; essentially it was pushing a composite signal out over the chroma pin of the S-video output.


But once I removed the two or three components used to bridge the signals like that, I get nice clean, properly isolated S-video and composite outputs through the device. 

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Posted (edited)

Some of these switchers do introduce interference due to either cable length issues, the quality of the internal wiring, or strange hacks to convert the signals from Y/C to composite or vice-versa.  Also, some mods are not terminated properly with a ~75ohm load, so they may not work properly on a longer cable.


One of my switchers (an RCA branded one I believe) will bridge the audio to mono if you only connect the left audio channel, so if I were to reuse that for a video signal I am sure it would cause a problem.


Edited by R.Cade

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