A few quick questions... (Atari modding related)

[cwilkson]

Next update.

 

I've just set up/found resistors for a decent luma-ladder, however, I'm worried it may be too far off. Here's what I have: 1 39k resistor, a 15k and a 5.6k resistor to form a 20.6k resistor, and finally a 5.6k and a 2.7k resistor to form 8.3k. That last one is the one I'm worried about, probably too far off. Chris, could you plot this resistor set-up really quick, that would be great.

Here ya go. Looks great.

 

The pink line is a straight line between your black and white. The blue line is the loaded output voltage. It's pretty linear. Good.

 

Also, now that I do have video, I can barely see a thing on any of my t.v.'s without turning brightness and contrast up to monstrous levels. This probably has to do with the lack of contrast mentioned earlier, and most likely, I have to build an amplifier of some kind to fix it. Mind verifying that for me?

Dead on.

Finally, I am also losing a bit of sync as when the picture faces dramatic changes (like changing the maze in Jr. Pac-man) the picure flips out and becomes a little wobbly towards the top. This, as I'm guessing also relates to the lack of much signal mentioned above. I could be wrong, so correct me if you must, but that's just my two cents.

Yep, I bet that's it. Your sync pulse is only 110 mV. That's pretty hard for most TV's to catch...they're expecting 287mV. Plus if there's any noise on the signal (typically from color crap being coupled in) the margin is even further decreased. Your TV might try to sync on random pixel #17 on line #48. Or whatever.

Wow, I sure have gotten quite a bit done on this lately!

It's a good feeling, isn't it?

 

-Chris

[Dragnerok X]

Separating the signals is a great thing. Good for you. Nothing but "happy" can come of that. The rest of this is a little confusing. Are you using 2 cables for video, one for luma and one for chroma? (you should be...or use a s-video cable) Oh nevermind, you mentioned an s-video cable. Did you disconnect the RF cable from the RF modulator before connecting so audio signal to it? You should, otherwise you're probably hurting the modulator. I know maybe you think you don't need it anymore, but why kill it?

 

-Chris

 

To clarify: Yes I'm using an S-video cable, the 4 pin version. Also, I've both removed the rf modulator and channel select switch as detailed in A.J's instructions.

 

I've been wondering a few things, though.

 

For one, I think I might of hooked up the S-video cable backwards. When I first saw the cable I imagined that the red wire was chroma and the white luma, but I wasn't able to get anything from my 32' RCA Console T.V. (hadn't used for the mod up until that point) Switching it got a picture, but based on the quality, I'm beggining to wonder. Tell me, can the signals of an S-video cable be reversed and still have a working image?

 

Second, Is 8.3k too far off the roughly double 10k, 20k, 40k luma ladder to hold accurate colors?

[cwilkson]

Separating the signals is a great thing. Good for you. Nothing but "happy" can come of that. The rest of this is a little confusing. Are you using 2 cables for video, one for luma and one for chroma? (you should be...or use a s-video cable) Oh nevermind, you mentioned an s-video cable. Did you disconnect the RF cable from the RF modulator before connecting so audio signal to it? You should, otherwise you're probably hurting the modulator. I know maybe you think you don't need it anymore, but why kill it?

 

-Chris

 

To clarify: Yes I'm using an S-video cable, the 4 pin version. Also, I've both removed the rf modulator and channel select switch as detailed in A.J's instructions.

Ok. Sounds good.

For one, I think I might of hooked up the S-video cable backwards. When I first saw the cable I imagined that the red wire was chroma and the white luma, but I wasn't able to get anything from my 32' RCA Console T.V. (hadn't used for the mod up until that point) Switching it got a picture, but based on the quality, I'm beggining to wonder. Tell me, can the signals of an S-video cable be reversed and still have a working image?

Nope. The TV expects Luma and Chroma to show up on specific wires. It won't work in reverse.

Second, Is 8.3k too far off the roughly double 10k, 20k, 40k luma ladder to hold accurate colors?

Well, due to the interactions we've discussed so far, 10k is actually *wrong*. The 8.3k will give better performance in fact (as shown in those plots above - the one showing 8.2k, 20k, 40k)

 

The beauty of (good) s-video is that the color information is well isolated from the luminosity (brightness) information. You can (and should) evaluate them separately, luma first. With that in mind, what's your s-video set up look like with the chroma wire disconnected? Or better yet, connected to ground? I.e. feed the TV zero volts on the chroma wire. Can you post a screenshot?

 

-Chris

[Dragnerok X]

Ok, Chris. I hate to say this, but my free time is getting a bit low lately.

 

 

I'm going to have to pick this project up later, but in the meantime, I'll clarify the picture.

 

The beauty of (good) s-video is that the color information is well isolated from the luminosity (brightness) information. You can (and should) evaluate them separately, luma first. With that in mind, what's your s-video set up look like with the chroma wire disconnected? Or better yet, connected to ground? I.e. feed the TV zero volts on the chroma wire. Can you post a screenshot?

 

I wasn't able to get a screenshot of this yet, but basically what it looks like is, with the color switch in black in white mode, normal pretty much. In color, a "grid" of solid black vertical lines appears where color would show on the screen. Does this mean the signals aren't separated?

 

 

I'm beggining to get a bit frustrated with this, you know.

[cwilkson]

I wasn't able to get a screenshot of this yet, but basically what it looks like is, with the color switch in black in white mode, normal pretty much. In color, a "grid" of solid black vertical lines appears where color would show on the screen. Does this mean the signals aren't separated?

 

 

I'm beggining to get a bit frustrated with this, you know.

 

It's hard to say what's happening without seeing a picture. But no rush. I know what it's like to have 17 projects and time for only 2 of them. Hmmm....work, eat, sleep....which 2 should I do today? I also know how it feels to get hooked into an ever expanding project. The CyberTech video card took away 4 years of my life. And it's not done yet.

 

-Chris

[Dragnerok X]

It's hard to say what's happening without seeing a picture. But no rush. I know what it's like to have 17 projects and time for only 2 of them. Hmmm....work, eat, sleep....which 2 should I do today? I also know how it feels to get hooked into an ever expanding project.

 

Definetly. I couldn't agree more. We Atariage Software/Hardware guru's should right a book about time management.

 

The CyberTech video card took away 4 years of my life. And it's not done yet.

 

-Chris

 

Not done? Are you hinting that the Cybertech Video mod may once again see the light of day?

 

BTW: Just in case you are wondering, here's what I'm working on now.

 

Edit:...and one post away from post 500, I've updated my avatar to celebrate.

Edited March 28, 2007 by Dragnerok X

[Jess Ragan]

Hey, can I combine the first two steps of Franzman's mod with the this one?

 

http://web.archive.org/web/20041024230629/...p/Question3.htm

 

Heckendorn's mod works, but rather poorly. There's vertical stripes throughout the display and the sound is miserable, with any sound effects drowned out by a harsh, obnoxious buzz.

[Dragnerok X]

Hey, can I combine the first two steps of Franzman's mod with the this one?

 

http://web.archive.org/web/20041024230629/...p/Question3.htm

 

Heckendorn's mod works, but rather poorly. There's vertical stripes throughout the display and the sound is miserable, with any sound effects drowned out by a harsh, obnoxious buzz.

 

You should be able to, however, you will have to use a different audio spot (closer to the tia source pin), due to the fact that quite a bit of audio circuitry is being removed; none-the-less (I know this from experience) this will result in much clearer audio. Also, the rf modulator removal should work fine with ben's mod.

Edited September 5, 2007 by Dragnerok X

[Jess Ragan]

Could I take the sound directly from the TIA? I'm looking at the schematic for the chip and there are two audio pins (12 and 13), presumably for stereo sound. Should I tie those two pins together and connect them to the sound port?

[Dragnerok X]

Could I take the sound directly from the TIA? I'm looking at the schematic for the chip and there are two audio pins (12 and 13), presumably for stereo sound. Should I tie those two pins together and connect them to the sound port?

 

Yes, that would work. Just remember to ground the cable you are using. Stereo works too with this setup, if you keep the signals separated.

[A.J. Franzman]

Could I take the sound directly from the TIA? I'm looking at the schematic for the chip and there are two audio pins (12 and 13), presumably for stereo sound. Should I tie those two pins together and connect them to the sound port?

Yes, that would work. Just remember to ground the cable you are using. Stereo works too with this setup, if you keep the signals separated.

That depends. If you want to pull the sound off the board, pins 12 and 13 are already connected. Like other 2600 outputs, they're open-drain (similar to open-collector from the TTL days); the output pin is either grounded or open. If you're using the board, the required pullup resistor is already there (if you haven't removed it). Then the audio line goes to a blocking capacitor before being injected into the audio mixer. You should take the audio signal directly from the mixer end of this capacitor -- Ben Heckendorn's so-called "audio spot" (lift this lead of the capacitor from the board if you want to isolate the sound from the existing mixer circuit to keep it cleaner).

 

If you're building something from scratch, you'll want to add back the pullup resistor and blocking cap. For a stereo circuit, keep pins 12 and 13 separate and do it twice. Use the same values that were on the board if you want it to sound the same. You do NOT need to change the resistor values for the stereo version as some modders have suggested.

Edited September 7, 2007 by A.J. Franzman