cx2600a rev 16 Video Issue

[linuxfanman]

Hello all. I was wondering if anyone might know whats going on.

 

I have a Atari Vader 2600A rev 16 board and I have video out of the RF Modulator but it seems fuzzy. Fuzzy might not the right word. For example, If I have the harmony cart in and its on the menu screen, you can see all these ghosted fuzzy boxes on the screen. The video is better on channel 2 then on 3. But they are still there. It seems to be artifacting from the sprites.

 

I have changed the following, C241, C242, A201, And A203. I have checked r217 at 24.3k and checked cr203 and it was good. The RF modulator is giving out a good 61.25Mhz signal. I also have a good 4.8v peak to peak sync signal on r217. So I'm at a loss. First atari I have ever seen with this problem.

 

Any Ideas guys, If I recall right the TIA (a201) is driven but the mpu 6507 in the 2600 as it doesn't have the ANTIC chip. Do you think the MPU could be the issue? I'm thinking maybe even L205 might be letting in some interference to the RF.

 

If replacing the MPU and inductor doesn't fix it, I will video mod it to see it there is a clear picture that way, but I am trying to avoid that because I am going to sell this Atari and already have alot, too much, invested in it.

 

If anyone out there can figure it out, let me know. I"ll put up pics if you guys need them..

 

 

Thanks....

[Mister-VCS]

It is a common problem with the 2600A... all 4-switch-systems I have seen so far have a fuzzy picture.

[linuxfanman]

Well it turned out to be the RIOT Chip. I'm assuming, the "fuzzy boxes" turned out to be caused by bad RAM in the chip. Funny though, because it passed the color bar and grey bar test on the DTC. Now that I have replaced the RIOT chip, the video is crisp and clear. Well, as good as RF video can get on an Atari that is.