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Atari 800XL no color


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I have an Atari 800XL that is going to a computer monitor via a composite cable. It has been working flawlessly for years.

 

The other day I left the 800XL on for about 18 hours. When I returned, the graphics were in black and white. I turned it off for a couple days and started it again and color was back.

 

Today I left it on for about 4 hours and it is giving me just black and white images again. I've checked that the monitor is not at fault, but I am not sure where to begin troubleshooting this. Are there terms that would help me run some searches to find other people with this problem?

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Turn on. Turn over. Upside down on the right side there is a small hole. It is color pot access. Put small eyeglass screwdriver in and turn wiggle back and forth. See what that does for ya. Word up.

 

Thanks, Paul. I turned the 800XL on this morning before work just to see the problem again and color was back. I will definitely look at that pot should that happen again. I didn't know about it, so I appreciate the information. I had left it off for about 8 hours... I guess this is a question for anyone, but are there components that could heat up and knock out color, to where letting it cool down for a bit would "fix" it?

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  • 3 years later...


hi Fred.

Without knowing the history there are some common mistakes people make by mixing PAL systems with NTSC monitors and vice versa, it can cause this problem. So try different monitors If you have them.
 

If the machine was working before then a few things to note. The GTIA can go bad partially, it provides the colours for the playfields gfx so I’d be looking at that. Also there’s a buffer between the GTIA and the video output. The signals ( lum, sync and color ) from GTIA are fed to a 4050 non inverting buffer before the output jack, they can go bad completely or partially too.

 

if you have a logic probe it can help by probing the outputs of the 4050 to see if the color signal is present.

Edited by shoestring
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I had one where the color pot failed....  if you can measure the resistance between the pins, there should be a center and two ends.  End to end should be the resistance of the pot, and as you move the pot, the resistance from the center to each end should change.  If any measurement is open, the pot could be at fault.

 

 

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4 hours ago, xrbrevin said:

on an unmodified 800XL, SVideo is monochrome

you have to do a small soldering mod to get colour

Hello xrbrevin,

 

Do you have some more info how to solder mod?

I have some 600xl wit uk version pal. It show allso black and white or is the monitor pins output different yoo 800xl?

 

Gr.

Marco

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11 minutes ago, marcokitt2000 said:

Hello xrbrevin,

 

Do you have some more info how to solder mod?

I have some 600xl wit uk version pal. It show allso black and white or is the monitor pins output different yoo 800xl?

 

Gr.

Marco

http://biosrhythm.com/?p=1002

 

There are other steps you can do to improve the video output but this is the simple starting place.

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On 11/7/2020 at 12:46 PM, marcokitt2000 said:

I have some 600xl wit uk version pal. It show allso black and white or is the monitor pins output different yoo 800xl?

Hi,

apology for my delayed response and thanks to @mimo for providing the 800XL mod.

attached is the PAL 600XL mod. it requires removal of 3x components, cut a trace and add a wire. you can add a 75ohm resistor to chroma and luma for a clearer display.

600xl pal svhs mod 1.jpg

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19 minutes ago, xrbrevin said:

Hi,

apology for my delayed response and thanks to @mimo for providing the 800XL mod.

attached is the PAL 600XL mod. it requires removal of 3x components, cut a trace and add a wire. you can add a 75ohm resistor to chroma and luma for a clearer display.

600xl pal svhs mod 1.jpg

Thanks, my previous 600xl had VBXE so I'd never done this mod. Will have to do it on my current 600xl

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3 minutes ago, mimo said:

Will have to do it on my current 600xl

initially i did the mod without the 75ohm resistors and it worked fine.

curiosity got the better of me so i fitted them afterwards but the difference was not apparent. i think it might depend on what screen you are using.

best of luck!

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On 11/10/2020 at 11:22 AM, xrbrevin said:

initially i did the mod without the 75ohm resistors and it worked fine.

curiosity got the better of me so i fitted them afterwards but the difference was not apparent. i think it might depend on what screen you are using.

best of luck!

Thanks fir all the good info.

Do you have foto's from the 600xl fix without 75ohm resistor?

 

And where must i cut the trace pin 5 and pin 2.

 

Thanks again fir all the info.

Than i can build 600xl with 64k upgrade and monitor cable.

Or is it beter remove tv tuner and add a svideo connector! is there allso foto picture for do it.

 

 

Gr.

Marco

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sadly i have no photos as i eventually treated the machine to a UAV mod ?

i recall one of the PCB tracks at the back of the 600XL monitor socket needs to be cut as from the factory it is tied to GND. I found this article that goes into more detail:

 

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  • 2 weeks later...
On 11/15/2020 at 5:04 AM, marcokitt2000 said:

And where must i cut the trace pin 5 and pin 2.

 

On 11/15/2020 at 10:39 AM, xrbrevin said:

i recall one of the PCB tracks at the back of the 600XL monitor socket needs to be cut as from the factory it is tied to GND.

The image below shows the solder side of a 600XL PCB, the trace which needs to be cut can be seen between pins 2 and 5 of the DIN5 PCB footprint.

post-3606-0-39960600-1457363026.jpg

Edited by BillC
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