7800 Service Manual and Controls?

[Everett1954]

Hi,

 

Does a 7800 service manual or schematic exist? If so could someone point me to them? What do the Potentiometers R57 and R58 on the main board do?

 

Thanks

[CPUWIZ]

http://atariage.com/7800/archives/index.html?SystemID=7800

[Trebor]

Schematics for the 7800 are here. There is no service manual for the 7800.

 

R57 controls the color pot of the 7800 graphics mode.

R58 controls the color pot of the 2600 graphics mode.

 

The color pots turn (counter)clockwise and are highly sensitive. These normally should not be touched and are set by the factory.

 

When factory tuned accurately, hues $1x and $15x/$Fx will match, resulting in ~25.7 degrees of separation between the various color hues. This will change as the console warms up; in depth coverage regarding the matter is found under http://7800.8bitdev.org/section entitled, Atari 7800 Color Documentation.

 

Some may choose to 'eyeball it' by comparing different game colors. This could become frustrating though, especially in light of the automatic color phase shifting that occurs [i.E. 24.7 -> 25.7 -> 26.7 -> 27.7], as detailed in the above link.

 

There is a Diagnostic cartridge that provides a more reliable way to adjust the 7800 color pot:

 

https://www.youtube.com/watch?v=hxl9tKzpP7U

 

More information about the Diagnostic cart is here. There is also an in-depth analysis.

 

The Color Bar Generator by Videosoft can be utilized for adjusting the 2600 color pot. Adjust the opening/title screen so the top half and bottom half screen border colors match:

 

Calibration ideally should be performed with a console 'cold' during the first minute of it being powered on.

 

*EDIT: CPUWIZ beat me to the 7800 schematics/archives link.

[+Mitch]

There is this: http://atariage.com/forums/topic/216763-7800-theory-of-ops-ts-guide/ as well.

 

Mitch

[Everett1954]

Thanks for the great answers and help! Glad I didn't touch them during my AV mod.

 

Does anyone sell the 7800 Diagnostic Cart ? Is the .BIN available to burn my own eprom?

[+Mitch]

I think Best Electronics still sells the 7800 diag cart. The bin for the diag and color bars are both available.

 

Mitch