Video issue

[panama800]

Take a look at this pic see a my 800xl is doin this?

 

Any help would be great.

[Paul Westphal]

Does it play Games?

Please post a pic of the power supply.

 

Looks like the ram. If it is made in Hong Kong it is socketed, so that means the chips pop right out.

If it is made in Taiwan, it's a box of chocolates.

Edited January 24, 2018 by Paul Westphal

[jmccorm]

Take a look at this pic see a my 800xl is doin this?

Any help would be great.

I'll speculate. [EDIT: Looks like Paul beat me to the punch and edited in his similar thoughts while I was typing this.]

 

The more that you can describe the video output, the more helpful it would be. Also worth knowing is how your monitor is connected to your 800XL.

 

I'm trying to interpret what I see in the YouTube video. It is difficult because we're interpreting intermittent problems that last for only a fraction of a frame... which is compressed by YouTube which doesn't preserve this kind of thing very well. To me, it *looks like* the problem isn't that the video output isn't being disconnected, but the ANTIC is grabbing bad data now and then and the GTIA is trying to rendering it? (Or the ANTIC grabbing good data, but the GTIA dropping the ball.)

 

*If* video memory is the problem, there might be a few reasons, including:

 

1. An intermittent-bad GTIA chip

2. An intermittent-bad ANTIC chip

3. Intermittent-bad memory support chips or components

4. Intermittent-bad memory chips

5. The ANTIC's HALT signal not (always) getting to the CPU (so bus data from CPU activity leaks onto the screen) [unlikely, but an interesting thought] ... so bad ANTIC, support chips, RAM, or even an intermittent-bad CPU...

6. Marginal power supply

7. Oxidized connections on ICs that need to be resocketed (a potential root cause for the other issues)

 

Hard to rule stuff out without swapping replacement parts in or out, but we're not at that point yet. What might illuminate the issue some more is to try different pieces of software. Do very large programs work just fine? Does a CPU-heavy piece of software make it worse or different? Do some pieces of software work fine but others don't? If so, are the ones that work disk or cassette based? Does the system sometimes have trouble even booting or running the self-test?

 

Do you have *any* other peripherals plugged in? (Can you unplug them for us?)

Has this 800XL been upgraded in any way? If so, when and how?

Do you have any spare / replacement components (including power supply) which can be swapped in?

Are there any other symptoms beyond video garbage? Do all programs work just fine?

Does the problem happen when you first turn the system on, or after it has been running for a while? I might recommend, as a test, putting the computer (and/or the power supply) in the refrigerator (but NOT the freezer) for an hour and then testing it, but someone is likely to explain that this is not healthy for the computer.

 

In BASIC, run this command (without quotes) "POKE 559,0" and describe what you see. Shake your Atari and see if it changes. Press the RESET button to recover (or turn the computer off and on again).

 

BONUS: If the previous command *had bad video*, then try this command and see if it acts differently: "POKE 559,0 : POKE 1536,2 : X=USR(1536)"

BONUS: If that previous command *did NOT have bad video*, but you still see the problems when you are just sitting in BASIC, repeat the above command without the first poke, so you would type: "POKE 1536,2 : X=USR(1536)"

 

NOTE: Both of these bonus tests will crash the 6502 but your ANTIC and GTIA will continue to run, access memory, and display video. The RESET button should recover the system and return control to you. If not, power it back off and on again.

 

Hopefully one of the above questions or tests will lead us in a better direction. (Also worth noting: once someone breaks the ice with technical specifics, usually you'll receive a few more messages with even better ideas!)

 

Hope this helps,

the jmccorm

Edited January 24, 2018 by jmccorm

[_The Doctor__]

try a different power supply

be good to see it hooked up to the monitor/tv different way

check capacitors, no shorts or opens on pcb

were you able to select AV test,

were you able to select ram test.

work backwards rf, gtia, antic, delay line, support, memory.

down load sams for your Atari

use a schematic that shows the transistors and their values.. they tend to be more reliable...

Edited January 24, 2018 by _The Doctor__