Gauntlet black level issues

dbstallman

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Now that my Simpsons board is 100%, I have turned my attention to my two Gauntelt boards.

The first one has a number of issues, but the first I want to tackle is a lack of grey scale. The colors, black and white are all fine, but there is no shading. The esiest way to see it is on the ghosts :


They don't get darker as they get weaker. You can also see it easily on Gauntlet logo on the title screen, the colors don't graduate from one to the other, they are just single solid bars.

I have the schematics and have found the circuits for red, green, and blue but nothing seems to indicate how the black level is controlled.

It's not the monitor adjustments either, that picuture is from my JAMMA cab that runs all other boards with out issues.

Thanks for the help,
Brian.
 
The first one has a number of issues, but the first I want to tackle is a lack of grey scale. The colors, black and white are all fine, but there is no shading. The esiest way to see it is on the ghosts. They don't get darker as they get weaker. You can also see it easily on Gauntlet logo on the title screen, the colors don't graduate from one to the other, they are just single solid bars.

I have the schematics and have found the circuits for red, green, and blue but nothing seems to indicate how the black level is controlled.

It's not the monitor adjustments either, that picuture is from my JAMMA cab that runs all other boards with out issues.

Yeah, that's not really "black level", technically. Black level is a monitor adjustment thing to set the point at which a "black" signal from the game JUST displays black, on the verge of becoming dark grey.

Shades of grey aren't independently displayed by the monitor. Every shade of grey (and white) are equal parts red, green & blue. White is full-blast of all three. The brightness of the grey depends on how high all 3 colors are set.

I may be a monitor setting issue. Not all games output video signals exactly the same, so just because it is "right" with one game on it doesn't mean it won't need re-adjustment with another game's output. Try turning down the "screen," brightness, or contrast (depending on what your monitor calls its settings.

If that doesn't do it, it's a PCB issue. Does test/diagnostic mode not identify any RAM or ROM issues?
 
Womble is right, it is a board fault. As I was staring at the schematics, though, I think I saw where my problem is, a 2149-3 RAM at location 10L. I am going to check for broken traces and shorts around it now.

I'll let you know how it goes.
 
I would agree with the board problem as well.
I know generally a video issue usually point to the left side of the board.
I've had glitches with my Gauntlet boards and it usually involves a rom or chip in that general area.
 
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