Star Wars - Color Issue (red is always firing?)

bungy

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My Star Wars seems to produce incorrect colors. This is a board issue because I have tried multiple known good 6100 monitors with the same result.

What I'm seeing is the blue is purple (magenta) and the green is yellow. Red shows up fine. It looks to me like red is firing for all colors (blue + red = magenta, green + red = yellow). I suspect cyan (blue + green) would show up as white. Haven't tried test mode grid screens yet, but I will confirm later.

In my searches I haven't found anything specific to Star Wars regarding this issue. Can anyone help?
 
I did some more checking... In test mode, the crosshatch screen cycles through the colors in this order:
Normal: Red, Green, Blue, Magenta, White, Yellow, Cyan
Mine: Red, Yellow, Magenta, Magenta, White, Yellow, White

Clearly it looks like red is being fired with every other color.

Another thing I noticed is that on the title and high score screens, there is a lot of flicker and the normal colors are all blue & green. The instructions screen (all red) has some flicker too, but I think that's normal. The scoring screen which is normally purple has no flicker and is very smooth. It almost seems as if it has no problem displaying red when it's supposed to, but when it displays other colors, adding red into the mix causes the flicker.

I am guessing there is a problem with the AVG board. Any ideas on where to look?
 
Not that familiar with the Star Wars boards yet. But if it's not the monitor. It might have something to do with the RGB transistors. Don't have schematics in front of me, so you'll have to do a little checking. But yeah sounds like red is always on, so that transistor may be shorted.. Just a thought.
 
Not that familiar with the Star Wars boards yet. But if it's not the monitor. It might have something to do with the RGB transistors. Don't have schematics in front of me, so you'll have to do a little checking. But yeah sounds like red is always on, so that transistor may be shorted.. Just a thought.

Thanks for the tip. I removed Q4 (red output) from the board and it tested fine. So I swapped it with Q5 (green) which also tested good, but there was no change in behavior.
 
Going further back in the circuit, there is a 7407N at 8L and an LS175 at 5L. I don't have the tools or expertise to test them, but would it be worth swapping them out? Or could the problem be further back?

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Are you using the EMI board? If so you might try removing it, it might be however unlikely causing cross talk between colors.

Never having had a color problem like this before I'm kinda of at a loss atm.
 
Are you using the EMI board? If so you might try removing it, it might be however unlikely causing cross talk between colors.

Never having had a color problem like this before I'm kinda of at a loss atm.

No, I don't have the EMI board. I'm going to try replacing the LS175 tomorrow as I found one on a parts board. I don't know what else to try so I might as well try something.
 
BINGO.

I stole a 7407 from my other Tron boardset and the colors came up correctly. Didn't bother with the LS175 as I wanted to go backwards in the circuit sequentially. Thanks everyone for the help, it is much appreciated!

SW_RGB_Buffers.jpg


If one of those buffers above was shorted to high (+) ie the top one, then the red would stay on all the time

All the best :)
 
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