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Wednesday 16 May 2018 at 07:05
It looks like C' is bad, but when you tested U-9 pin 6 and 8 were low. When I look at the manual pin 6 is D' and pin 8 is A'. Something doesn't add up. I checked my machine and U-9 pin 7 is the C' on mine which matches the manual. Could you have checked the wrong chip?
Source: http://pinside.com/pinball/forum/topic/1986-sys-11-high-speed-police-light-not-working/page/2#post-4400540