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Monday 19 March 2018 at 10:26
The topic that you linked where U206 is called the same type as U201 is probably mixed up with another U20x.
Function of U206 is to read the dedicated switches and (according to schematics) it should be a 74HC245
With an HCT273 installed, I can imagine that (some) datalines are stalled
74HC245.jpg
Source: http://pinside.com/pinball/forum/topic/tried-fixing-tspp-tv-now-blanking#post-4288487