12 replies to this topic

[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]

NeilTheDruid, on Sat Jun 11, 2011 10:20 AM, said:

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.

Attached Thumbnails

• 

Edited by NeilTheDruid, Sat Jun 11, 2011 1:23 PM.

[GroovyBee]

Not on this schematic :-

http://www.atariage....00_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]

GroovyBee, on Sat Jun 11, 2011 4:11 PM, said:

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 by NeilTheDruid, Sat Jun 11, 2011 6:00 PM.

[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 by NeilTheDruid, Fri Jul 8, 2011 6:57 AM.

[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.