2600 with interesting picture problems

[Hiddenevil]

Hi everyone

 

Not been on here for a while, but i've unboxed the Atari six switcher and got back in to playing my favourites

 

Though i seem to be having a slight issue with the picture. I'll do my best to discribe the problem.

 

If insert Keystone Capers, Pressure cooker i get the following picture which will settle down to a very faint bar scrolling up the screen.

 

 

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At it's worst it takes the form of two 2" bars of static noise, top and bottom of the screen with the picture pulling and scrolling.

 

At first i thought it was the power switch on it's way out. I've taken the console apart, used switch cleaner and tested the lines on the board with a volt meter. The circuit seems fine. I have also tried the atari on a Vega 1970's B/W portable, which gives me a perfect picture and also a more modern flat screen LCD TV, which also gives a nice picture.

 

However my girlfriends TV seems to have a beef with the old atari and i have to fiddle with the power switch till i can get a stable picture and it doesn't always last. I can be 5 minutes in to a game and the screen will start to scroll a little.

 

However the behaviour seems to also be effected by the game i insert in the Atari. One cart will give a perfect picture and another will give the scrolling.

 

Any thoughts?

[RevEng]

Each 2600 game has the freedom to construct the frame a bit differently than any other game. With the 2 games you mentioned, the only slightly non-standard thing I see is they turn on blanking during the overscan part of the frame.

 

What games are stable? Do you Harmony or some other way to run homebrew?

[Hiddenevil]

Bowling is another game that suffers. Q-bert is one game that is perfectly fine. No i've not got one of those cartridges yet, i only read up on them a few nights ago. My gf moved in to a new place and the Atari has been sitting in a box in the bedroom waiting to be used, as we both love playing on the thing.

 

I'm currently looking at Pressure cooker and the picture is fine, but if i start playing it, i'm pretty sure i can bet that 10 minutes in to a game the picture will start to flick, scroll at random..oh and i get a slight buzzing noise through the speakers.

 

P.s I dont have an home brew games

Edited March 8, 2012 by Hiddenevil

[Hiddenevil]

The picture seems to stablise after 5-10 minutes of the fresh cart being inserted, but there still remains a 1 inch barely visible bar scrolling up the screen. I'm just wondering if this is something to do with the TV and not the 2600. I've had it apart, i've pressed all the chips down, just in case that was the cause. I've twiddled the screw on the RF modulator which doesn't seem to do a lot aside from move it off channel.

 

I dont think the power switch is actually causing the problem now.. :-/

Edited March 8, 2012 by Hiddenevil

[RevEng]

I think your TV is just particularly sensitive to the non-ideal frames that some 2600 games produce.

 

I looked at bowling, and it turns on vblank before vsync too, where q-bert turns it on at the same time. (as it should) I haven't heard of early vblanking causing a problem like this, but that's the only pattern I'm seeing so far.

 

If you have another non-passive device to run it through first, like a VCR, you might try that too.

[Hiddenevil]

Im beginning to think your right. Luckily we do have a DVD/VCR combo at her flat, so i'm going to try passing the 2600 through there

 

Thanks for all the help, been very handy!

James