Inexpensive Transistor Based AV MOD

[Zybex]

Schematic

 

 

 

[*]R1 1,5 Kilo Ohms

[*]R2 2,7 Kilo Ohms

[*]R3,R4 5,6 Kilo Ohms

[*]R5 39 Kilo Ohms

[*]R6 500 Ohms

[*]R7 22 Ohms

[*]R8 100 Ohms

[*]Q1 Transistor 2N2222 (You can use a 2N3904, but quality suffers)

 

Questions :

 

- Who is TIA?

 

TIA is a processor of ATARI 2600. You must look for pins 2,5,7,8

 

- How i can get 5v?

 

Use a multimeter, and get the 5v from the voltage regulator.

 

- How i can get ground?

 

Wow, try any metal shields inside

 

Some pictures (not of my property) :

 

TIA pins, chroma and audio >>

http://www.cheeptech.com/2600mods/2600mods.shtml

 

Transistor :

http://www.electroflash.org.nz/images/npn.gif

http://www-ece.rice.edu/~jdw/figs/2n3904b.jpg

 

Sorry about my english

[Zybex]

http://www.fairchildsemi.com/ds/PN/PN2222A.pdf

 

2N2222 Datasheet

[Jacob Rose]

Cool!

 

A few weeks ago I did a resistors-only composite hack based on the one posted on AtariAge, with help from Stella list archives and schematics of the 2600A to find the right pins, but this looks almost as simple, so I might give it a try. Can you explain what's going on here for those of us who haven't made a transistor circuit since high school? =)

[Zybex]

The schematics is here :

[n8littlefield]

Ok, so I'm looking into ordering the parts for this mod - but was wondering does 1,5 = 1.5? 2,7 = 2.7? Just want to make sure I order the right parts.

 

Thanks!

[Atari-Jess]

Ok, so I'm looking into ordering the parts for this mod - but was wondering does 1,5 = 1.5?  2,7 = 2.7?  Just want to make sure I order the right parts.

 

Thanks!

 

I would say yes because he's in Chile. (many countries use , instead of .)

[lbaeza]

Hi

 

Here's the list with some more familiar notation:

 

[*]R1 1.5K Ohms

[*]R2 2.7K Ohms

[*]R3,R4 5.6K Ohms

[*]R5 39K Ohms

[*]R6 500 Ohms

[*]R7 22 Ohms

[*]R8 100 Ohms

 

Regards

[n8littlefield]

Thanks for the input. Now, can anyone tell me why I cannot find a 500 ohm resistor? Does anyone know of an online source? I found some great kits of resistors, with all of the ones needed included, but the closest they come is 560...

[spongebue]

get some smaller ones and wire them in series (that is, 1 after another) if they add up to 500 (or close to it) then you are good to go. Of course, you could wire some resistors up in parallel, but then the math gets a bit complicated to figure out which one you need

[Susuwatari]

Just wire 2x 1K resistrs in paralell and you'll get 500 ohms. And yes the math is complicated if you use mixed resistors in parallel but if all the resistors in parallel are the same, you just divide the resistor by the total number in the circuit. In this case, 1000/2 = 500.

[christianscott27]

i feel like i should know this already but...

 

has anyone come up with a way to make an A/V out for the 7800?

[krupkaj]

I have got my first VCS last week. It is 2600 jr. with some games.

 

It has quite nice video through RF, but I would like to have composite and audio output. I like this modiffication, but I have question. My 2600 jr. is PAL Will this mod work with my PAL machine? In case it is for NTSC only do anybody know how to modiffy my one?

[+batari]

Just want to give a warning to anyone who tries this mod. I did it, and it worked and gave a sharp picture, but the whites and bright colors were way overdriven, to the point that I had to crank the contrast to a minimum and turn down the brightness, and they are still a little too bright.

 

Ben Heck's 2.0 mod is very similar but uses different resistor values. When I get a chance, I'm may swap out the resistors to his and see if it works any better.

 

Or, if anyone can suggest a way to fix the existing circuit to change the output of the brighter colors to a more tolerable level, let me know.

[+batari]

Or, if anyone can suggest a way to fix the existing circuit to change the output of the brighter colors to a more tolerable level, let me know.

877809[/snapback]

Hi, I just experimented with changing the resistor values, and found that R8 is too small... I changed it to 250 ohms and the whites are no longer overdriven. Actually, all the colors look better now.

[krupkaj]

Thanks, but will that work with my PAL VCS?

[+batari]

Thanks, but will that work with my PAL VCS?

878766[/snapback]

It would probably do something, but wouldn't work very well since the resistor values were chosen for NTSC color signals. However, here is one I found that reportedly is made just for PAL, which is essentially the same but with different resistor values and tapping off of pin 6 instead of pin 8 of the TIA.

[krupkaj]

Thats it. I have read somewhere that PAL TIA has different pinout than NTSC one. I will try it and the let you know what it does. Thanks for scheme.

[keilbaca]

Exactly right. Pin 8 for NTSC, pin 6 for PAL. Should work fine

 

Glad to see that the mod was going good for you guys, but I also had the too bright problem. Thats when I just went to straight resistors, thus the mod I offer at the marketplace.

[gizmomelb]

Thats it. I have read somewhere that PAL TIA has different pinout than NTSC one. I will try it and the let you know what it does. Thanks for scheme.

878777[/snapback]

 

Hi Krupkaj,

 

as another PAL Atari owner I was just wondering how the PAL modification went? Was the picture output clear or did it need modifying?

 

Thanks,

Gizmomelb