RGB bypass amp on SF Jr. not working

[Joonas Suomalainen]

Hi!

I installed the RGB bypass amp 4.1 into my Super Famicom Jr., but I’m not getting any signal into my ODV-GBS-C. I’m using a PackAPunch CSYNC 470 Ohm SCART cable. I first tried it with just the J2 jumper closed and then with J3 closed too. Then finally with both open. The ODV-GBS-C isn’t recognizing any signal no matter how I wire it. The cable works with my other Super Famicom and I’m pretty sure it has CSYNC coming in from multi AV out pin 3. The scaler works with all my other consoles. I also know for a fact the console powers on and is running the game.

Can anyone point out where I might have made a mistake? Is there anything I could do to pinpoint the problem? If nothing else works, is it possible to wire R, G, B and CS into the S-RGB chip instead of the S-CPUN chip? I know the S-RGB is where you’d normally tap for S-Video, not RGB SCART, but I saw one guide for an older amp board that had CSYNC wired from the S-RGB chip straight to multi AV pin 3. Could I try that?

• This topic was modified 5 months, 2 weeks ago by Joonas Suomalainen.

[Joonas Suomalainen]

I did some testing. If I put a jumper wire between the CS pad and multi AV out pin 3, the scaler picks up the CSYNC and I get picture and sound as intended. Also, if I put a jumper wire between the CS pad and the left side pad of J3, the scaler picks up the CSYNC. So does this mean the problem is that the CS pad isn’t connected to the right side pad of J3 internally? How would I test why this is the case? Or is the problem something else entirely? The picture looks great—and to my eyes exactly the same—whether I connect CS directly to pin 3 or the left side pad of J3. The weird thing is that J2 is now open, which should result in an image that’s too dark because I’m using the 470 Ohm CSYNC SCART. So I’m also bypassing J2’s resistor when I connect CS to J3?

[BuckoA51]

I’m sorry nobody seems able to help. I can clarify a little about the csync jumper at least. These boards were designed quite some time ago and back then it was much more common to find incorrectly wired SCART cables on the market. These cables would simply pass through the sync signal without proper attenuation. While a lot of TVs would tolerate this, it wasn’t exactly a good idea as it was driving their input voltages higher than the recommended spec and could cause wear and tear and premature death.

J2 is for sync attenuation only, it doesn’t affect brightness.

The thinking was that if you installed the board and forgot to set the jumper, you would either get a perfect picture (with a bad cable) or no picture (with a cable that properly attenuated the sync). That’s much better than forgetting to set it and damaging your TV.

These days almost all cable shops know to properly attenuate the sync in their cables, so you should solder jumper J2 shut unless you explicitly picked up a cable without the attenuation resistor, often sold as a “TTL cable”.

If you still don’t get a picture after verifying all this, check your cable has the correct attenuation resistor.

Jumper J3 is for enabling buffered csync which you will need with the cable you are using. Follow step 5 on the instruction page:-

Nintendo RGB Bypass Amp (Revision 4.1b-VGP)

SNES cables either use composite video for sync (pin 9 on the SNES end) or composite sync (pin 3 on the SNES end). If your cable was sold to you as a “CSYNC cable” then it’s using pin 3. Remember pin 3 on PAL consoles is a straight plus 12 volts so make sure you’ve corrected that first if you have a PAL console.

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