Smeared Video on an AV Modded 7800

[DistantStar001]

I recently did an AV mod on an Atari 7800. Everything works, except the video looks as it someone smeared the image to the right. At first I thought this was a grounding issue, since the ground trace on the bottom of the board did come off, but when I bridged the lead there was no improvement. I've tried re-soldering the connections, but that didn't help either. I checked the board for solder bridges, and shorts, but didn't find any (which was not surprising, since the does boot properly, and loads both 2600, and 7800 games). I've tried multiple televisions, and tested each television with multiple consoles (a 2600, Coleco Gemini, Intellivission II, NES, SNES, Genesis, and Master System). The 7800 is the only console giving me this problem.

 

 

Recently I've tried probing the board with a piece of wire, bridging the video, or ground to other points on the board to see if there was a weak connection, or damaged trace, still nothing. So I'm basically running out of ideas. Has anyone ever run into this issue before? And if so, then how did you fix it?

 

 

My sincere thanks to anyone who can help.

[+Mitch]

Do you know which AV mod is installed?

 

Mitch

[Osgeld]

stick your finger on the mod board (it wont hurt there's not enough power in there) you will get a ton of interference but if the smear goes away its a input or output capacitance issue

 

also measure the resistance tween video out and ground, cant tell you how many times I thought something went wrong just to find out the damn cable I got out of my box was not making good ground contact with the TV ... ideally it should be around 75ohms

[DistantStar001]

The AV mod is a simple composite, with mono audio. there is a third resister between the video out, and ground.

 

 

As far as touching the board goes, I managed to get the interference, but the image was still smeared.

 

Sadly I don't have a working multimeter at the moment.

Edited March 10, 2018 by DistantStar001

[DistantStar001]

I figured it out! There was a slight bridge between the 5v and video on the board. I cleaned it up and now my picture is perfect.

 

Now I just have to figure out how to fix the pause/black and white button.

[+-^CrossBow^-]

I figured it out! There was a slight bridge between the 5v and video on the board. I cleaned it up and now my picture is perfect.

 

Now I just have to figure out how to fix the pause/black and white button.

Well, you could try and carefully lift the white plastic that goes around the actual button on the top of the switch and clean the contact pads under it. But I think it is more reliable to just replace the button completely. In fact, when I have one button that causes issues, I usually replace them all out with newer.

 

Here is where I go for the exact match on the cheap. But I've also got a small stock pile of Alps brand switches I picked up from Mouser I believe that cost more each, but were rated for longer life.

 

https://console5.com/store/tactile-switch-12mm-x-4-5mm-atari-7800-power-pause-select-reset.html

[Osgeld]

https://www.mouser.com/ProductDetail/612-TL1100D

[DistantStar001]

thanks.