colors off on 7800

[MrBeefy]

Just got a 7800 working and noticed the colors are a little off from my other one. I know on the 2600 there was a knob I could twist to adjust color. Is there anything like that on the 7800?

[Trebor]

Just got a 7800 working and noticed the colors are a little off from my other one. I know on the 2600 there was a knob I could twist to adjust color. Is there anything like that on the 7800?

 

Short Answer: Yes. There are two color pot adjustments on the 7800 board. You need to remove the metal shield. The one closest to the cartridge port is for the 7800. The one below it is for 2600 colors.

 

 

Long Answer: Before adjusting, keep in mind that all Atari consoles (2600/5200/7800 colors) phase shift (Most noticeable some greens turn tan/brown) over time. In other words, as the console "warms up" some colors change (and some more significantly than others).

 

Additionally, the same console may result in different colors on a CRT as opposed to a modern display (Again, most noticeable will be some browns being greenish). Your display's hue/tint also plays a significant role regarding it.

 

Ideally, you want to use the Diagnostic cart ($25 at B.E.) to adjust the pot as it is *highly* sensitive:

 

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

 

The ROM image for the above to be utilized on the actual hardware is here: Diagnostic Test Cartridge (19xx) (Atari) !.bin

 

The ROM image for emulators (Same file above, just with a header) is here: Diagnostic Test Cartridge (19xx) (Atari) !.a78

 

Note: The ROM will only run under MAME/MESS (0.159 is the current public gold standard), as all other 7800 emulators are too inaccurate to run it properly, if at all.

 

Last, but certainly not least, RevEng has created an updated Diagnostic/Utility ROM that features many useful functions and tests, including a match strip for the color pot adjustment. It is much more robust and useful than the above original. It's not finished yet, but certainly looking forward to getting that on cart once completed.

[+DrVenkman]

Great info, Trebor. That reminds me, I need to adjust mine. From looking at PCB of my 7800 when I disassembled it last year, I presumed one of those was for 7800 games and one for 2600 games. Good to see I was correct in that assumption and to see which is which.

Gee, it would be great if we had some kind of modern flashcart to use those roms with actual hardware, say like a 7800 version of the Harmony ...

 

(Still patiently waiting for the Concerto ... *sigh*)

[Trebor]

Glad you found it useful Dr.

 

If you need to adjust the 2600 pot, just use the Color Bar Generator ROM from Video Soft: Color Bar Generator.bin

 

All you need to do is match the border color on the top and bottom halves of the screen:

[Note: Capture(s) intentionally demonstrate a ~26.2 degrees phase shift; ~0.5 degree delta between top and bottom]

 

 

Obviously, the ROM works in Stella. Works great under MAME/MESS too:

 

 

Load the same ROM onto any Harmony cart, as it works fine on a 2600 or 7800 console for adjusting 2600 colors.

[MrBeefy]

 

Short Answer: Yes. There are two color pot adjustments on the 7800 board. You need to remove the metal shield. The one closest to the cartridge port is for the 7800. The one below it is for 2600 colors.

 

7800_POTS2_REDUCED.png

 

Long Answer: Before adjusting, keep in mind that all Atari consoles (2600/5200/7800 colors) phase shift (Most noticeable some greens turn tan/brown) over time. In other words, as the console "warms up" some colors change (and some more significantly than others).

 

Additionally, the same console may result in different colors on a CRT as opposed to a modern display (Again, most noticeable will be some browns being greenish). Your display's hue/tint also plays a significant role regarding it.

 

Ideally, you want to use the Diagnostic cart ($25 at B.E.) to adjust the pot as it is *highly* sensitive:

 

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

 

The ROM image for the above to be utilized on the actual hardware is here: Diagnostic Test Cartridge (19xx) (Atari) !.bin

 

The ROM image for emulators (Same file above, just with a header) is here: Diagnostic Test Cartridge (19xx) (Atari) !.a78

 

Note: The ROM will only run under MAME/MESS (0.159 is the current public gold standard), as all other 7800 emulators are too inaccurate to run it properly, if at all.

 

Last, but certainly not least, RevEng has created an updated Diagnostic/Utility ROM that features many useful functions and tests, including a match strip for the color pot adjustment. It is much more robust and useful than the above original. It's not finished yet, but certainly looking forward to getting that on cart once completed.

 

Thanks for the info! When I played One-on-One the court was a greenish color instead of brown. Didn't seem to change as it was on. :/ 2600 colors are good though.

[Trebor]

Thanks for the info! When I played One-on-One the court was a greenish color instead of brown. Didn't seem to change as it was on. :/ 2600 colors are good though.

 

The dominant floor color in "One-On-One" is F3 under a color palette chart. Typically, the "F" (Hue 15) values are primarily influenced by the color phase shift degrees and secondary by hue/tint controls.

 

If another 7800 connected to the same display shows a nice brown, instead of green, then that pretty much seals the deal, it is not a tint/hue issue and a color pot adjustment is probably needed.

 

The console in need of adjusting may be hovering around the low/low-mid 20's (~22-24 degrees) even after a warm up (10-20 mins continuous running); as opposed to a factory tuned console which would be around the mid 20's (~25.7 is factory perfect), ultimately reaching the upper 20's (~27-28 degrees) after warming up.

 

To correct this, the top pot should be turned to the right/clockwise. Adjusting the pot to the right/clockwise increases the color phase shift degrees of the console. Turning to the left/counter-clockwise decrease the color phase shift degrees of the console.

 

A very slight adjustment is likely required - meaning 1/32-1/16" increments. The dial is extremely sensitive. IMHO, having one of the aforementioned (ROM) tools is nearly mandatory to ensure the console is adjusted properly.

[MrBeefy]

Thanks and yeah the other system is brown on same TV. This might be a project for me today after I'm done working at the comic shop!

[Andromeda Stardust]

Just wanted to give a heads up. I recalibrated the color on my Best AV 7800 earlier tonight. I ran the color bar generator on my harmony cart, selected green screen, and dialed it in until the blue and red phosphors on the CRT were completely shut off. I loaded Pacman 4k on both consoles (Harmony and AA cart). Now perfect colors on my 7800 (2600 mode) AV and it matches my 4-switch woodgrain RF perfectly when switching between RF and composite on the TV.

 

Unfortunately when I first calibrated the 2600 colors I accidentally twirled the wrong pot and fudged the 7800 hue adjustment...

 

I don't have a color bar app for 7800 so I used PMP Pacman Collection using the blue of the maze as pure blue, then ghost colors to tweak. Cherries are cherry red. Pacman is yellow. Inky is cyan, not greenish, not blueish. Anyway, after tweaking to my liking, I resealed the RF shield and screwed down the case.

 

Voiding the Best warranty was worth it! They really do not want you to tamper with the console: red wax on the screws, hot glue plugging the screw hole, and "warranty void if removed" sticker to cap it off!

Edited July 31, 2015 by stardust4ever