Atari 800XL Cold Start purple color issue

[donjn]

Just purchased an Atari 800XL with the Super Video 2.1 mod for s-video. Now, my s-video cable is on its way and should arrive today or tomorrow, so I have been playing around with composite.

 

When the Atari has not been on for a while, off of a cold start it has a purple color to it. here is the transition:

 

• I tested this with two different cables all giving the same result
• Pretty sure it is not the monitor as it does not happen with anything else.
• Once the color is correct it does not turn back to purple at all and stays blue.
• Need to try new power supply to see if that is the cause
• This only happens if the unit has been off for a while, more than 15 minutes.

So with this, I have some questions.

 

I have a 30 day window to return this item

• Would you keep or return an Atari 800XL that does this?
• What if with s-video mode this does not happen?
• Is this a sign that something serious is going to happen to this unit down the line?

Thanks!

 

 

 

 

[+DrVenkman]

Generally, there is a typical color shift that happens as systems warm up over time. I think the extent of color shift is being exacerbated by the monitor you’re using, but having said that, it could also be that there’s a capacitor inside that is getting marginal. Usually warm up time for some degree of color shifting is just a couple minutes.

[donjn]

Generally, there is a typical color shift that happens as systems warm up over time. I think the extent of color shift is being exacerbated by the monitor you’re using, but having said that, it could also be that there’s a capacitor inside that is getting marginal. Usually warm up time for some degree of color shifting is just a couple minutes.

Are you saying this is normal or is this possibly something that could get worse?

[+DrVenkman]

Are you saying this is normal or is this possibly something that could get worse?

I’m saying some degree of color shift is normal as the system warms up. The extreme shift from purple to blue might be the sign of a capacitor issue inside the machine or something, but it might also just be the flat panel display you’re using. Do you have a CRT you can connect to the computer for a test?

[+tf_hh]

Just purchased an Atari 800XL with the Super Video 2.1 mod for s-video. Now, my s-video cable is on its way and should arrive today or tomorrow, so I have been playing around with composite.

 

When the Atari has not been on for a while, off of a cold start it has a purple color to it. here is the transition:

• Need to try new power supply to see if that is the cause
• This only happens if the unit has been off for a while, more than 15 minutes.

• Would you keep or return an Atari 800XL that does this?
• What if with s-video mode this does not happen?
• Is this a sign that something serious is going to happen to this unit down the line?

 

I assume you use a NTSC computer, right? The color changing is typical for NTSC - PAL looks different.

 

A little bit color changing after warm-up is normal, but this is a little bit too heavy IMHO. But the problem is, without checking the power (or changing the power supply) you can´t determine exactly which one is the culprit.

 

The GTIA - one of the two graphics involved chips in your Atari - generates the color signal. To set up the internal color generator of the GTIA, there´s an external voltage up to 7 volts needed. For setting up the value, there´s a pot (variable resistor) in the lower left corner of your Atari. This one controls the value of these voltage fed to the GTIA.

 

The connection to the issue you showed is: This voltage is made using a voltage loading pump fed with the inverted output of the system clock from the CPU ("PHI1"). GTIA reacts very sensitive to this voltages. Changing the pot a very very little bit can turn the whole screen to purple, green or disable color.

 

So three culprits are possible:

 

- The pot itself

- The GTIA (the color setting will change with every other GTIA you put in, there are never two same GTIA, that´s the reason why Atari includes this set-up circuit)

- The power supply

 

Using any Atari XL/XE (except the 1200XL) will have different colors when used with different power supplies, specially when not genuine ones are used.

 

So first should be a test with another power supply. When it´s the same effect with another power supply, the computer has a (little) problem. Won´t you fix it by yourself, then return the device.

[donjn]

Thanks guys I have a new power supply. I will conduct a test:

• Use a CRT
• s-video connection through the LCD
• new power supply

Changing one at a time until I narrow down the issue.

 

Thanks!

[Forrest]

I had a similar problem years ago on my 800XL. Fixed if by popping the case (power off), noting the position of the pot and rotating it back and forth 3 times - returning it to the original position.

[donjn]

Help me here. What is the "pot"?

[Forrest]

Pot is short for potentiometer

The one I referred to in my post was next to or part of the RF modulator. I'm not familiar with the Super Video 2.1 mod - it may have it's own pot.

[+Nezgar]

The 'Pot' is short for 'Potentiometer' / an adjustable/variable resistor. Here's a picture that shows where it is on the 800XL motherboard.

 

You can actually adjust this without opening the computer at all, there's a small hole that accesses it from the underside of the computer. But that might be harder to mark where the starting position was.