Quoted from arolden:Finally, success!
I replaced U4, U9, U10, U11 and U2 with no improvement. Then I decided to replace U13 which had caused other display artefacts as described in my other thread: https://pinside.com/pinball/forum/topic/gottlieb-system-3-vertical-lines-on-display
And it worked!
It is odd that on the 2 display drivers I have repaired recently, U13 has been the problem on both. It looks like a common failure point and I'll be replacing it before U4 in future.
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It's always nice to see another person that actually enjoys Tee'd Off. About a year ago I replaced my DMD with pin2dmd and started learning to colorize it. There are still parts to do, but it's sure looks good in color.