S-video mod best practices...

[Yoder]

Hey guys,

I recently added an S-video mod to my Model 1 Genesis and it worked great. I did the amp on luma only with a 2N3904 and I put 220 uF capacitors on both the luma and chroma lines along with either 68 or 75 ohm resistors (can't remember which I had).

I have some things I'd like to change, though. I used non-shielded wire on the luma and chroma lines, and I did not solder the transistor directly to the CXA1145. Instead, I extended it a few inches and wired everything above the board. However, I now understand that this can introduce noise/interference that you'd then amplify with the transistor. I'm going to redo this, soldering the transistor directly to the video encoder and probably use some shielded cable (from an old RCA cable?) for the luma and chroma runs to the S-video port...I think Tiido suggested this somewhere. I also connected to the bottom side of the board for a cleaner look. Is this a good or bad idea?

Anyways, I wanted to see if you guys had any other recommendations for the S-video mods for the best signal output?

Thanks!

[Lastcallhall]

Personally, I've used nothing but the Jaxmazon mod for all my model 1 s-video needs:

http://www.sega-16.com/forum/showthr...l=1#post294849

It's simple, it's small, and it's effective.

[Yoder]

Thanks, this is basically the exact mod I did, but I think I used 75 ohm resistors for both lines. But the question I really asked was the logistics of the wiring, etc. ie..

1. Solder transistor directly to video encoder legs
2. Use shielded cable
3. Use common grounds? Best place to get it? Edge of board, etc?
4. Best place to get 5V? Off 7805, off CXA1145, etc?
5. Solder to bottom of board or to CXA1145 legs on top surface of board?

Thanks...

[Lastcallhall]

Thanks, this is basically the exact mod I did, but I think I used 75 ohm resistors for both lines. But the question I really asked was the logistics of the wiring, etc. ie..

1. Solder transistor directly to video encoder legs
2. Use shielded cable
3. Use common grounds? Best place to get it? Edge of board, etc?
4. Best place to get 5V? Off 7805, off CXA1145, etc?
5. Solder to bottom of board or to CXA1145 legs on top surface of board?

Thanks...

1) You can - I've always used a short wire (1-2 inches MAX) to give me some wiggle room in placing the circuit inside the Genesis
2) I've used CAT5 UTP cable without an issue. The rainbow banding is more prevalent in the VA2 and VA 3 models over the VA6, but this is a known issue not inherent to shielded cable from what I understand. My VA6 looks gorgeous on my 50" projection.
3) I always take the grounds from the edge of the board, that way I don't risk messing up other components by trying to solder onto them.
4) Best places I've found are the 7805 and on the AV out. You can pull it from the master oscillator too, but that's kind of far from everything you need 5V for.
5) I always solder onto the top of the chip - it keeps the wires short and away from any solder points that can tear the cable on the bottom.

HTH

[Yoder]

Awesome, thanks! Big help...

I forgot about the AV out having 5V...cool. Yeah, I didn't see any artifacts outside of the va3 rainbow banding...

[GohanX]

I was wondering about where to get something like a 26 gauge wire that was shielded. Cat 5 cable is brilliant and cheap. I did a RGB mod on my Turbografx CD and it has some slight interference issues, this might work. Not sure if I want to bother fixing it though.

[Lastcallhall]

It's worth a shot. I mean, Monoprice has 25' of Cat 5e UTP for $3.33, and shielded for $5.74 (although they're currently out of 25' - other sizes may be available), so the cost plus shipping isn't that big of a risk. Plus, you wind up with usable cable for a while. I bought 25' a couple months back and I'm only about half way through it.

[Mamejay]

I just use the following amp. Uses 2 x 2n3094 transistors and 2 x 27 ohm resistors. Works perfectly for MD1, MD2 and SMS consoles.
SegaS-videor.gif

[Yoder]

I think this was sort of the original version of the mod, but it really comes down to personal preference and the TV used. You're actually amping chroma and using lower ohm resistors, so the picture will be much brighter than the version lastcallhall and I are using.