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Friday 9 March 2018 at 08:39
Hi,
U3 is the DSPROM, it's a 512 KB - 27C020.
As the board boot, you can be sure that the GAL U8 is OK (as it decode the address map for RAM/ROM/VIDEO, if it's burned, nothing work ! but it's not the case).
The RAM (U4 - 6264 - 8KB), is shared between the video chip (U2 - 68B45) and the cpu (U1 - 65...
Source: http://pinside.com/pinball/forum/topic/gottlieb-system-3-vertical-lines-on-display#post-4271408