Clearpic2 on a 1200xl question

[yorgle]

I just finished the Bob Woolley? video fix (the 10 component version) on one of my 1200xl's. Before the mod, I was able to run a monitor cable to the video in on a tv and get a color picture. Now all I get is black and white (but really nice and clear). Is this a monitor cable issue or have I screwed something up with the mod? I noticed that the mod says to replace the capacitor at c62 but my 1200xl doesn't have one there? It doesn't look like there ever was one there to begin with so I didn't put one in. Could that be the problem?

 

BTW, this is the modification I followed: http://www.atarimuseum.com/computers/8BITS...1200clrpic.html

Edited February 20, 2008 by yorgle

[+Larry]

I just finished the Bob Woolley? video fix (the 10 component version) on one of my 1200xl's. Before the mod, I was able to run a monitor cable to the video in on a tv and get a color picture. Now all I get is black and white (but really nice and clear). Is this a monitor cable issue or have I screwed something up with the mod? I noticed that the mod says to replace the capacitor at c62 but my 1200xl doesn't have one there? It doesn't look like there ever was one there to begin with so I didn't put one in. Could that be the problem?

 

BTW, this is the modification I followed: http://www.atarimuseum.com/computers/8BITS...1200clrpic.html

 

Hi Yorgle-

 

Sounds very familiar... Check out this thread:

 

http://www.atariage.com/forums/index.php?s...=107018&hl=

 

-Larry

[yorgle]

Well, I tried a different monitor cable and still could only get black and white. I then stuck a paperclip in where c62 should have been and WOW! Nice, crisp clear color. Obviously, I need to stick a capacitor in there, but I'm still puzzled as to why there wasn't one there in the first place. It makes me want to pull apart my other 1200xl's and see what they have.

[+Larry]

Well, I tried a different monitor cable and still could only get black and white. I then stuck a paperclip in where c62 should have been and WOW! Nice, crisp clear color. Obviously, I need to stick a capacitor in there, but I'm still puzzled as to why there wasn't one there in the first place. It makes me want to pull apart my other 1200xl's and see what they have.

 

I keep meaning to do a side-by-side component comparison of Clearpic2 and Clearpic2002. Maybe this serve as the motivation I need. I like Bob's sense of humor on 2002 "Version 128.3."

 

Glad it works for you. Can you do S-video in addition with your TV? I remember that when I made the 2002 mod, I could get composite color, but no S-video chroma.

 

-Larry

[yorgle]

Well, I tried a different monitor cable and still could only get black and white. I then stuck a paperclip in where c62 should have been and WOW! Nice, crisp clear color. Obviously, I need to stick a capacitor in there, but I'm still puzzled as to why there wasn't one there in the first place. It makes me want to pull apart my other 1200xl's and see what they have.

 

I keep meaning to do a side-by-side component comparison of Clearpic2 and Clearpic2002. Maybe this serve as the motivation I need. I like Bob's sense of humor on 2002 "Version 128.3."

 

Glad it works for you. Can you do S-video in addition with your TV? I remember that when I made the 2002 mod, I could get composite color, but no S-video chroma.

 

-Larry

 

My TV doesn't have s-video. I played around with it this morning and found that with a wire in place of C62, I get a perfectly sharp, clean image, but the colors are washed out, particularly the reds. Using a 4.7uf capacitor at C62 gives nice colors, but adds some slight ghosting. I'm going to buy an assortment of capacitors and see if I can find a happy compromise. Does anyone know if there is such a thing as a variable capacitor?

Edited February 20, 2008 by yorgle

[+bob1200xl]

Sure - they have variable capacitors in lower values. You might want to try a variable resistor, instead. Using a 4.7ufd capacitor is pretty much the same a piece of wire at color clock frequencies - you just block the DC bias to the transistor.

 

C62 is a negative feedback path that was used to tweak the bandwidth of the color amplifier. In the original circuit it wasn't required. In this hack, it is.

 

None of these video modifications are really perfect. If you try to draw really solid video out of a 1200XL, you get ground bounce - nasty noise in the CHROMA and LUMA.

 

Bob

 

 

 

Well, I tried a different monitor cable and still could only get black and white. I then stuck a paperclip in where c62 should have been and WOW! Nice, crisp clear color. Obviously, I need to stick a capacitor in there, but I'm still puzzled as to why there wasn't one there in the first place. It makes me want to pull apart my other 1200xl's and see what they have.

 

I keep meaning to do a side-by-side component comparison of Clearpic2 and Clearpic2002. Maybe this serve as the motivation I need. I like Bob's sense of humor on 2002 "Version 128.3."

 

Glad it works for you. Can you do S-video in addition with your TV? I remember that when I made the 2002 mod, I could get composite color, but no S-video chroma.

 

-Larry

 

My TV doesn't have s-video. I played around with it this morning and found that with a wire in place of C62, I get a perfectly sharp, clean image, but the colors are washed out, particularly the reds. Using a 4.7uf capacitor at C62 gives nice colors, but adds some slight ghosting. I'm going to buy an assortment of capacitors and see if I can find a happy compromise. Does anyone know if there is such a thing as a variable capacitor?

[yorgle]

Bob1200xl: Thanks. I'll give the variable resistor a try. In any case, even with the slight ghosting, the image is way better than it was stock.

[yorgle]

After messing around for about an hour with various capacitors and resistors, I finally settled with a 2.2k resistor at C62, which gives a very good compromise between color saturation and image sharpness. Thanks to everyone for their input.