Desperate modder needs help finishing s-video mod.

[NeilTheDruid]

Hi guys I've been building an s-video mod from this thread. Using post #1 for hook ups and #15 for the amp circuit.

 

As you can see, I am having some problems. I have the chroma lines down, the colour looks spot on. I also have the luma lines pretty sorted, with the brightness being exactly where I want it. The bit that I'm tripping up on is the sync line. I have gotten a great picture from my 2600 carts but I cannot get the 7800 games to stop flickering. I have no idea why this is.

 

The original posters hook up point for the sync line doesn't work well at all with my console so I tried moving it to pins 9+10 of the LS32 above the MARIA on the board which results in the pics displayed in post #30 of the thread above.

 

Any suggestions would be massively appreciated.

[GroovyBee]

The original posters hook up point for the sync line doesn't work well at all with my console so I tried moving it to pins 9+10 of the LS32 above the MARIA on the board which results in the pics displayed in post #30 of the thread above.

 

You mean pin 11 for SYNC#?

[NeilTheDruid]

I've got the wire jumped from pin 9 and 10 (soldered together). Should I have it connected to pin 11?

[GroovyBee]

LUM1 from MARIA and LUM0 from TIA will not get you SYNC#

[NeilTheDruid]

According to the schematics pins 9+10 of the LS32 above the maria are directly connected to the directly connected to the sync pin of the tia and maria respectively.

Edited June 11, 2011 by NeilTheDruid

[GroovyBee]

Not on this schematic :-

 

http://www.atariage.com/7800/archives/schematics_pal/Schematic_7800_PAL_Low.html

[NeilTheDruid]

Sorry groovy, the schem I've got must be incorrect. I tried hooking the sync to pin 11 but it made a flickery mess, worse than what I previously got.

[NeilTheDruid]

I've checked against the schematic that groovy linked and it doesn't seem to apply to my board. The one I uploaded on post #5 seems to apply to my board. With this in mind where would the best place to pick up the sync be? I've already tried pin 8 on the LS32 (U13C) and I tried jumping across 9+10 in the same position.

[GroovyBee]

Shorting two outputs together isn't a good idea. Maybe you've killed MARIA in some way?

[NeilTheDruid]

Shorting two outputs together isn't a good idea. Maybe you've killed MARIA in some way?

 

I don't think so because the composite mod that I have on the board still works perfectly. I think you're right though, shorting the two points together probably isn't a great idea. I just did it just to see if it worked. It's like I'm missing something, I could solder directly to the marias sync pin and I still get the flickering.

Edited June 12, 2011 by NeilTheDruid

[NeilTheDruid]

Ok, I've just tried the same mod on my other 7800 and I am still getting the same results, so it must be something to do with the mod circuit. This is really starting to kick ma brain in the face!

[NeilTheDruid]

Wooo! I have some success finally! I decided to dismantle the mod I have been doing above and instead I tried the saundby mod. Which seems to working pretty well. I just have to make some slight adjustments. At the moment the colour seems a bit washed out. I'm not sure if this is something to do with the brightness or with the chroma. In general, most of the colour looks a bit "whiter" than it should be. Did use a 100nF ceramic cap instead of a 1uF tantalum on the chroma line. Would this be the cause?

 

Any suggestions on where to change the circuit below would be much appreciated.

 

Edited July 8, 2011 by NeilTheDruid

[gdement]

I started working on an SVideo mod on a breadboard a very long time ago, which I must admit I never finished. I have a habit of not finishing things, often because of scope creep.

 

Anyway, I started with Saundby, except I hooked up only the 7800 signals, no 2600.

The most helpful modification I found was to put a 74HC4050 buffer on the luma+sync signals. Without that, you get a major pinstriping effect in luma. You can somewhat tweak that with the luma pot but I wasn't happy with it. Using the buffer chip was a major improvement.

It's not very noticeable on a CRT but on an LCD it's more significant.

 

I experimented with using an amplifier circuit on chroma but I never decided if it was helping or not. From what I remember I think it slightly helped my problem of color artifacts on edges of objects, but didn't really solve it.

 

As far as the washed out look, I'm not sure. I was planning to try using Atari's original resistor ladder values on LUMA, instead of the reduced values that Saundby used. I think LHE mentioned that this was a factor in making it look washed out, but I haven't tried it.