Modding the Snes so the Tototek GBA-SNES adapter does not need separate AV cable.

Whoho - I did it! It was not the microcontroller! It was the PAL-specific output circuit of the composite video! The only way to circumvent this was to cut an invisible trace. The picture is taken directly at the multi av out.



@stefan: I used a crappy board to test this cut

 

Man you're like a blind sniper...

 

Good job!
Ahh, the SNES and its enamel burried traces!

I did not think to bring it up but you definitely need to isolate the Composite output right at the AV port and put the transistor switch across the cut, at least this is how I did it. Otherwise you risk something like this happening.

 

You guys finally made this mod a success - Thank you so much!

Does this even mean you can still use the boards that you have designed?
Maybe I will get my fully modded Super Nintendo soon...

Whoho, that´s all I can say!

 

Well, here is a picture of my final installation.



from the second schematic on page 1 post 1, I made two changes:
- C1 is completely removed as the cap is not needed for the microcontroller there
- I replaced C2 by a 10k resistor.

Best

btw: I plan to publish the PCB (on GitHub and OSHPark) together with the pic-code (on GitHub) if this is fine with MaxWar

 

Yeah sure, go ahead and publish it! Im glad this mod is getting some use after all.

I do not see why you replaced C2 by a 10k.
The purpose of the C2 cap and the Q3 transistor was to sink the video signal from the SNES to ground, through a cap. But only when you use the adapter.

The reason I made this is that even though the transistors are supposed in theory to act like a perfect switch, I found that they don't. Even when they are supposed to not transmit I would still get a thriffle of signal going through. The snes encoder still outputs a black screen and sync signal through the composite output even when no games are being played, or when you are using the AD adapter for that matter. This thriffle of sync signal would produce interferences on my screen when I was using the adapter.

My solution was to ''sink'' it to ground via a capacitor. Using a 10k there kinds of defeats the whole purpose.

Edit: Although I do not remember precisely, this might be why I added C1 too, I guess it reduced the interferences.

 

Maybe it has something to do with the PAL-mainboard. I tested some different caps at C2 - from 18pF up to 100nF - and observed some kind of a degradation with increasing value. In the worst case with 100nF I had a black/white blurry picture instead of a colored stable one. After your post, I also tested some resistors as well as caps and resistors in parallel and in serial there. It turned out that the single resistor of around 580Ohms (not the 10k) is the best (in my point of view)... On a NTSC-board, it might be different again.

I see your intension with C1. I removed it because I have used a microcontroller instead of the logic element. The interference came up with the first NAND-gate at the expand-line which has some leakage current as the expand-line is not tied to ground in case of the adapter use. With the microcontroller I have the output decoupled from the input anyway and no leakage current which influences the state at the bases of Q2 and Q3.

 

Can´t wait to receive my GBA modified SNES

I highly recommend borti4939´s mods - he is a hardware wizzard !!!

 

Hey,

Super new here. Registered just to post this. I know this thread is at least a year old, but I'm hoping someone is still active who can provide some assistance, as I'm currently attempting the composite-only version of this mod, and I've run into a minor issue:

Spoiler

As far as I can tell, SNES output works fine, but output from the Super Retro Advance shows like the above (That's the title screen for Mario & Luigi Superstar Saga).

My electronics skills are still fairly basic, and this is definitely the most complex project I've taken on, but I'm trying to do this right. I've built everything on a protoboard, and I haven't (yet) cut any traces on the SNES (I'm not using the AV port yet, just trying to display composite from the output directly). I need some help trying to figure out what I've done wrong.

I'm 99% sure I've followed the diagram on page 1 correctly, but just in case, here is a pic of my build:

Spoiler

Any help or advice is much appreciated!

 

Small update: I'm now 90% sure my build above is wrong. I've re-wired everything so now I'm sure the circuit is right.

Unfortunately, the current state is the GBA Adapter works fine, SNES outputs a black screen.

I've traced the EXPAND line on the SNES board, and it doesn't appear to go... anywhere. Unless I missed something, there is no pull-up resistor, and for me, the line remains low when using a standard SNES cart.

This puts me back at square 1: Trying to find a way to detect when the GBA adapter is inserted, vs a normal SNES cart.

 

Yet another update: So EXPAND is being pulled high, but for some reason goes low when I attach the output to the TV.
I'm really stumped as to why this is happening.

I've tested each part of the circuit individually, and it appears to work fine. All three MOSFETS work as expected, as does the NAND gate IC,

Really hoping someone can help me out here.

 

Hey there borti4938,

The image from the earlier post is no longer appearing on the thread. Would you happen to still have it so I can try this mod out? I was lucky to snag one of these adapters brand new well after they stopped making them. Any help would be greatly appreciated.

 

On this, question. Can scart work?