PAL SNES + LM1881 = glitches?

[kendjet]

Hi all,


My apologies if this has been posted before, and I hope I understand things right since I only started reading about this stuff very recently


my setup:
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I have a PAL 2-chip SNES which I'm trying to connect through a Crosspoint 300 series matrix switcher. I bought a PAL SNES with Sync on luma cable, connected it through a female scart to 4BNC cable with built-in sync separator (LM1881) into the Crosspoint. Then the crosspoint is connected to 2 TV's (both using an UMSA) and some broadcast monitors (using BNC)


the problem:
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This works fine but I have some "glitches" every 10 seconds or so. It is more noticeable on one TV than on the other, and it's also harder to see on the monitor.


testing I've done:
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# when I remove the cable with the LM1881 in it and route the signal through a Sync Strike, I get the same problem, which is quite obvious since the Sync Strike uses the same LM1881 afaik.
# when I plug the Sync-on-luma cable straight into the TV, I don't have the problem, so the cable looks to be OK
# when I try to route the same signal (that already went through the LM1881) through an Extron RGB 201 Rxi, the problem remains (flipping the DDSP switch on the Extron even causes the picture to start rolling and I don't know why)
# this leads me to believe the problem is being caused by the SNES in combination with the LM1881


my question:
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I was thinking about 2 possible things I might try to fix this:

a) remove the cable with the LM1881 in it and try to route the signal into my Extron RGB 201 Rxi before going into the Extron Crosspoint. The only thing I'm wondering is how I would be able to connect the female SCART to 4BNC cable into the Extron RGB 201 Rxi, since the Extron only has a VGA input. Can I use a VGA to 4BNC cable and connect it to the other cable using simple connectors like these ones? http://www.electronix.com/images/82-160.jpg. So it would then look like this:

PAL SNES with sync-on-luma SCART cable -> female SCART to RGBs (4BNC) cable -> BNC connectors -> 4BNC to VGA cable -> Extron RGB 201Rxi -> Extron Crosspoint

b) if the above doesn't work, I might need to get a SCART switch instead for my SNES



Any other suggestions are more than welcome,

Thanks in advance!

[Darksakul]

PAL SNES with sync-on-luma SCART cable -> female SCART to RGBs (4BNC) cable -> BNC connectors -> 4BNC to VGA cable -> Extron RGB 201Rxi -> Extron Crosspoint

I think part of your issue is you have a Scart cable going into a BNC cable going into a VGA cable.
I am assuming other than the LM1881 you have no other circuity altering your image.

Consider trying to go with the least amount of cable adaptions as possible.
I know the Pal SNES Euro Scart cable have resistors on the RGB lines for attenuation (the NTSC version has capacitors instead).
I don't consider attenuation an alternation of the signal.

Maybe what you could do is have a Scart to VGA cable and skip the BNC cable entirely.
I do also know that certain BNC video cables don't work with the 15khz RGB with C Sync instead of VH (or separate) Sync.

Is your BNC cable the 4 wires or the 5 wires version? The issue is the 4 wire version from certain supplies do not carry over C-sync (as its not carried over to the correct pin).

The other thing I might say is skip any LM1881 sync filtering as not all TV sets like the "cleaned" sync from a LM1881.

[theclaw]

My limited understanding is composite video (CVBS) sync is the de facto standard for consumer SCART TVs.
Try that first if you have yet to establish your setup needs something else.