Atari 800XL Video Issues

[Bxbop]

I got my first Atari 800XL but it has some video gremlins. I'm going to need some help identifying the problem. I am new to this so I would rather be punching keys than tinkering with it. The Ready screen is distorted but if I insert a game cartridge it's fine. I only have Defender and it clears right up. The original power supply is putting 5.2V as it should and using the Monitor out to AV cables at the TV. Can somebody provide me some schematics for any chips I need to look at? Also reseated most all of the chips since they're all socketed.

 

Edited August 8, 2023 by Bxbop

[Beeblebrox]

100s of posts here on fixing these issues but it looks like it could be a bad transitor in the video circuit (a 2N3904 NPN), or look at the 4050 IC, then the GTIA and ANTIC chips.

 

Ages ago I had a 130XE with problems similar to this which I helped with the forum's advice. Check it out:

 

 

 

In my case (for a 130XE) it was a combo of a Q3 transistor issue and pin 2 of antic chip, plus other issues caused by bad ram.

 

EDIT: just a guess but perhaps pushing a cart in might be helping a loose contact on a socket make contact. You might have a dry solder joint somewhere, perhaps on the ANTIC or GTIA. Also worth cleaning (detox/contact cleaner) the sockets.

Edited August 9, 2023 by Beeblebrox

[xrbrevin]

welcome!

thats a nice 800XL - fully socketed and ceramic RAM too 😎

 

you need to advise what method you are using to connect the display.

 

standard hardware hierarchy:

1. RF modulator is the most inferior
2. monitor port composite is better
3. monitor port s-video is best (be aware that the chroma signal is not connected on stock 800XLs - you have to do a small mod to rig it up)

 

beyond these 3 factory options, there are many modern upgrades should your heart desire. they require some modding skills to install tho. VGA, HDMI, UAV are among them

[manterola]

You also need to consider the TV set... Maybe it is having problems synch-ing with the "weird" Atari video signal. I had an old early Magnavox LCD TV that struggled with the Atari Video signal depending on what was displayed on the screen.

 

[Beeblebrox]

30 minutes ago, manterola said:

You also need to consider the TV set... Maybe it is having problems synch-ing with the "weird" Atari video signal. I had an old early Magnavox LCD TV that struggled with the Atari Video signal depending on what was displayed on the screen.

 

I don't think the defender cart would display ok if it were TV issue.

 

Edit: 

"depending on what was displayed on the screen."

 

ahh,  - you may have a point.

Edited August 9, 2023 by Beeblebrox

[manterola]

12 hours ago, Beeblebrox said:

I don't think the defender cart would display ok if it were TV issue.

 

Edit: 

"depending on what was displayed on the screen."

 

ahh,  - you may have a point.

Probably you're right, but feeding the Atari signal to another tv should be something easy to do to discard that possibility.

[Bxbop]

Appreciate the leads Beeblebrox. The transistors checked out as far as I can tell. I floated a couple 3-4 soldier points and checked the rough parts of the board for continuity (some pcb blistering is starting to occur). Seems to be okay.

I'll test with other TVs next because I might some low quality AV cable. If I wiggle them at the TV, it appears to alter things somewhat, so will want to retry this.

 

Then, I have a GTIA chip on the way to replace or resale.  So I'll look to update soon, good or bad. :^)