No Sync with SNES

[B-Fake]

Hi all, I’ve finally got all the stuff together to bring the old SNES to life on the big screen and haven’t quite got it to work yet. I’ll try to provide as much info as I can to make figuring this out easier. When connected via SCART I get a greyscale test pattern looking thing from the OSSC on the TV, but no matter which input on the OSSC I switch to, the OSSC screen says NO SYNC (I’m guessing it should be AV1 RGBS that’s the one that works for c-sync SCART). Just for the hell of it, I tried the old original composite video cable in the green YPbPr jack and got a black and green picture on the AV2 RGsB channel so I think I can assume the TV will accept the signal. The TV does also put out a picture with the SNES hooked straight in to it via the composite RCA connections.

The signal chain is just SNES–>SCART cable–>OSSC–>HDMI cable–>Samsung LED TV.

Here’s details on the SNES
Original fat US SNES, no mods
From what I can gather without opening it up going by the serial number it’s an earlier SHVC-CPU-01 board so no 1CHIP, but I’m pretty sure that still outputs c-sync RGB (everything I’ve read says ALL fat SNES’s do), but if not, that’s the board/chipset it has.

And the cable
Super Nintendo CSYNC SCART shielded grounded cable from Retro Access
Has 330 ohm resistor on the sync line (they state this is for UN-modded SNES’s and to NOT use it with a MODDED SNES with a 75 ohm sync output)

Now having read more details in the OSSC wiki, it says the OSSC video and sync inputs have 75 ohm termination. I have a very basic understanding of electronics so I don’t know what 75 ohm termination means, but could the 330 ohm resistor on the sync line in the cable be the root of the problem here? Is there even any correlation between modded SNES 75 ohm output and OSSC 75 ohm termination or is it just coincidence? Again, pretty basic understanding of electronics here, lol. It’s the only idea I had and hoped to get some more knowledgeable input before I started modifying a brand new cable without knowing for sure it will fix the problem. Thanks in advance for any help!

[paulb_nl]

The 330 Ohm resistor is correct for a CSYNC cable on unmodded and properly modded consoles. It works together with the 75 Ohm termination in the OSSC to reduce the voltage.

The only possibilities are your SNES not outputting CSYNC (unlikely unless its a 1-CHIP-03), defective RGB cable or defective OSSC. You can rule out the OSSC by trying another console on the SCART input.

Another possibility is that you changed H-PLL Pre-Coast and Post-Coast settings but even then you should be getting occasional sync.

[B-Fake]

Hi, thanks for the reply. I would hope neither the OSSC or cable are defective as I bought them new from the source. I’ll still check the cable for continuity and the solder joints just in case. I’m new to this so I only have this one SCART cable, but I’ve got a N64 and Game Cube I could try with it. Will those still work with SCART in their un-modded state? I know I won’t get RGB, but at least composite would give me a signal. I did mess with some settings trying to get a signal so what are the H-PLL settings supposed to be in case I screwed them up?

[Harrumph]

You can use Reset Settings to change back to defaults.

Defaults are also noted in the wiki.
http://junkerhq.net/xrgb/index.php?title=OSSC#H-PLL_Pre-Coast

I think it might be too early to rule out the console is somehow defective in its csync output, testing the composite video doesn’t say anything about this because the signals are not taken from the same source on the board afaik.

[paulb_nl]

That would be helpful if you can check the sync line for continuity and measure if the resistance between the console end and SCART end is actually 330 Ohms.

Unfortunately only a few N64 have CSYNC connected and Gamecubes not at all according to RetroRGB.com

[B-Fake]

Ahhh, so even if i get a composite signal through SCART with the N64/GC it won’t tell me anything since that doesn’t use the csync anyways. When I get home from work I’ll restore the OSSC settings and take a multimeter to the cable. I’m sure one of my friends has to have another SNES laying around that I could try as well.

[B-Fake]

So after comparing pinouts it turns out the SCART cable was wired wrong. The wires going to pins 18 and 20 were swapped. After some quick work with the soldering iron it’s up and running beautifully! Thanks for the help troubleshooting this!

[paulb_nl]

Wow fortunately nothing was damaged. Pin 18 is ground and CSYNC output from the SNES is around 3 volts. The resistor on the sync line probably protected the OSSC.

The 330 Ohm resistor is connected to pin 20 now right?

[B-Fake]

Yup, everything is where it should be now. I’m really glad it didn’t cause any bigger problems. I should probably contact Retro Access to let them know. I’m perfectly happy with the cable otherwise, looks reasonably well made and no audio/video noise at all.

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