Atari 7800 AV/Composite Mod

[Vipp]

Hi all, i am looking for a little help.

I asked Scrappysphinx to help me attempt to mod my Atari 7800 (Rev C Pal) to output via composite instead of RF.

We have found a guide online that says its compatible with the Rev C and proceeded to use the diagram below to build a small circuit. Now the output seems to work fine on both scrappysphinx's lg & philips LCD TV's but not his samsung. I have tested the console in my own home on a Samsung & Philips LCD tv and a bush & goodmans CRT TV. I get no signal on the LCD tv's and on the CRT TV's i get an image but it very dark and i can only just see it. Audio output is perfect no matter which tv its hooked up to.

Pics

 

[SkydivinGirl]

I don't know about the Atari 7800 A/V Composite Mod, but I know that my Colecovision had the same problem when I modded it. Fortunately, the mod designer (Ben Heck) included a variable potentiometer that could be adjusted to fix this issue. Perhaps the same might be needed for your mod?

I know this might not be the case, but I thought I'd offer up a possibility. Good luck!

Heather

 

[TheCorfiot]

I have looked at the thumbnail above and if that is the pcb layout you have followed then it is very wrong i'm afraid....the transistor collector is not connected to the supply and your composite output should be coming from the emitter....

Try drawing it out by hand for me, it really isa basic emitter follower amp you are trying to construct..

TC

 

[Vipp]

Thank you for the advice Guys, i will see if scrappy can help me get a drawing of whats happening in the machine, im new to electronics but its very interesting and im learning fast.

 

[scrappysphinx]

Hey Bas, initially i followed the diagram below but got no video output at all, perfect sound though. I then found the above diagram on the atariage forum so i gave that a try and it works perfect with a very sharp picture on two, the LG & Philips, out of three of my TVs (my Samsung has struggled to display most of my retro consoles). Thats why i hotglued it and returned it to VIPP.

 

[TheCorfiot]

Hiya Mike

The stripboard layout in post 1 is defnitely wrong but I cant see any issues with the diagram in your post...as long as you followed that schem...

I would suggest adding a 20ohm resistor between the 5v and collector of the transistor to improve compatibility....


Using the stripboard diagram above, add 20ohm resistor in 5a to 5b
Move compoisite output point to 7d.

If you guys have no luck I can knock one up on stripboard for vipp...

Keep us posted
TC

 

[Stedy]

Hi,

Your connection points look ok but as others state the transistor needs power.

Have you tried the Atari 7800 S-video mod?
http://saundby.com/atari7800mod/7800_vidmod_construction.html
It works well and when converted to Component video, the 7800 video looks very sharp

Attached is a photo showing the video and audio pickoff points for the Rev C PAL Atari 7800.

Ian

 

[TheCorfiot]

Can guarentee this mod works well guys...

My 7800 is very happy for it, no pcb used either

TC

 

[scrappysphinx]

Thanks for letting us know Bas. Will take another crack at it soon. Just not got to it yet

 

[TheCorfiot]

Mate, send me the board and I will do it for vipp foc.
I have a neat method of installing it directly to the mobo after removing the rf modulator, no pcb involved or link wires just 3 output leads...

TC

 

[scrappysphinx]

Just to dig up an old thread, i tried this modification again and all seems to now work fine.

Guess it must have been me

 

[TheCorfiot]

Dope

 

[scrappysphinx]

Always buddy

 

[Vipp]

What was wrong with it mike? just a wire missing or something?

 

[mamejay]

I actually performed this mod last week also and all worked perfect. One extra thing I did was disconnect the top 2 resistors where the lum and sync are located. Cleared the picture up as best I could get it

 

[steflaet]

Hello,

I have a 7800 PAL VERSION and a kit for a RCA MOD.
A friend gives me the MOD because his 7800 have a PERITEL and he doesn't need this MOD. He will buy a S-VIDEO MOD.

I can't find good PDF to do this modification.

On my Chip "RCA ATARI" there is 4 pins on the left and 3 on the right.

Left side :
1 : AUDIO
2 : +5
3 : VIDEO
4 : GND

Right side :
5 : AUDIO OUT
6 : VIDEO OUT
7 : GND OUT

I don't know if it's correct because I found on the net a lot of montage with differents issues.

Can you help me for my ATARI 7800 PAL VERSION ?
On my Motherboard, how can I do ?

Because I found this :


But it's for a simple Audio OUT :


My MOD is for Red and White Audio + Yellow Video :






Thx.