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 Interesting SNES revision find

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WiiFitPlus



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PostSubject: Interesting SNES revision find   Thu Aug 08, 2013 11:06 am

So a few weeks ago I tore the hair out of my head, trying to figure out why I wasn't getting a picture out of my SNES.

I was doing the mod where I completely bypass the encoder to help rid of the vertical bar. This mod is done by doing the following:

First, lift the legs of red, green, and blue output pins on the SNES encoder. This ensures your SNES is not receiving the RGB signals at the A/V port from the encoder.

Tap the red, blue, and green inputs on the encoder. Solder the Texas Instrument RGB amp (same one used on the N64 RGB mod) and solder the outputs to the A/V pins on the back of the SNES.

Just like the N64 RGB mod calls for, wire up 5V, ground, and a capacitor between the two.

So anyway, last time I tried it a few weeks ago, I got absolutely no picture. I had no idea what could be wrong. So now, I got a new amp, and a new 1CHIP SNES, and the same deal. No picture. However, this time it was a bit different.

The picture would show up for a second or two, and as soon as something bright came up on the screen, the picture would go away. For example, the entire intro to Final Fantasy VI would play fine. But if I popped in Super Mario World 2: Yoshi's Island, I'd lose the picture as soon as the bright and colorful intro began playing. Weird!

Knowing that it must be a syncing issue, I soldered pin 7 of the SNES encoder directly to pin 3 of the SNES' A/V port (pin 3 of the SNES' A/V port is for sync). Same issue. However, going by a different guide, I soldered pin 7 of the encoder directly to pin 9 of the A/V port, as it explained that pin 9 is composite. It worked!

This is a bit odd to me, as composite is clearly wired up in the newer SNES systems. It appears that Nintendo stopped wiring up CSYNC for some unknown reason. Why? It can't possibly actually cost money, so who knows. Even stranger is that wiring up CSYNC again did not work for me when going to pin 3 of the A/V port. However, in my setup, wiring an SNES mini up with CSYNC to pin 3 works just fine!

I can't explain it, but for anyone having issues, or simply anyone wanting to do this mod, you have to wire CSYNC from the SNES encoder to pin 9 on the A/V port to get a picture if doing the RGB encoder bypass mod. Hope this info is helpful to someone out there!
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Drakon
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PostSubject: Re: Interesting SNES revision find   Thu Aug 08, 2013 11:36 am

You should never lift the legs on the built in encoder, just solder onto them.  For my onechip I probed where the multi av port connects to on the pcb and disconnected one side of the surface mount resistors / caps.  You posted that you "tap the rgb inputs of the encoder", after lifting them that would give you no picture.  The image is generated by the ppu which is fed into the encoder.

Which pin you need to wire sync to depends on how your rgb cable is wired, some of them grab sync from the csync pin, some from the composite video pin. Nintendo probably stopped wiring up csync because rgb tvs strip the sync from the composite video signal.
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WiiFitPlus



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PostSubject: Re: Interesting SNES revision find   Thu Aug 08, 2013 11:42 am

Drakon wrote:
.  You posted that you "tap the rgb inputs of the encoder", after lifting them that would give you no picture.
Nope, I lifted the RGB outputs, and soldered the amp to the RGB inputs (the opposite side of the encoder). I never lift the input pins.
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PostSubject: Re: Interesting SNES revision find   Thu Aug 08, 2013 11:43 am

Oh I see I misread that, still the way I did it I didn't have to lift any pins of the encoder. The way I did it is more complicated it requires probing and a lot of guessing where the signals go on a masked pcb.
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PostSubject: Re: Interesting SNES revision find   Thu Aug 08, 2013 5:24 pm

Drakon wrote:
Oh I see I misread that, still the way I did it I didn't have to lift any pins of the encoder.  The way I did it is more complicated it requires probing and a lot of guessing where the signals go on a masked pcb.
Yep. If someone is uncomfortable lifting pins, another method would be to desolder the entire A/V port so you remove it from the SNES motherboard. Then you bend the R, G, and B pins so that they no longer touch the motherboard. Wire your R, G, and B lines right to the A/V port.
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PostSubject: Re: Interesting SNES revision find   Thu Aug 08, 2013 10:26 pm

OnyxDomain wrote:
Drakon wrote:
Oh I see I misread that, still the way I did it I didn't have to lift any pins of the encoder.  The way I did it is more complicated it requires probing and a lot of guessing where the signals go on a masked pcb.
Yep. If someone is uncomfortable lifting pins, another method would be to desolder the entire A/V port so you remove it from the SNES motherboard. Then you bend the R, G, and B pins so that they no longer touch the motherboard. Wire your R, G, and B lines right to the A/V port.
Yeah instead of doing that I probed to where those pins connect which is one surface mount resistor and one surface mount capacitor for each pin.  I just desoldered one side of each resistor and cap and it works great.  It's less destructive but requires probing and knowledge of the typical snes pcb layout. I'm just trying to think of the least destructive approach.
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