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Thursday 11 January 2018 at 09:09
Replace both capacitors C20 and C21 at the CPU board (1uF ceramic). They tend to loose their capacity over the years narrowing the Watchdog window. This watchdog is monitoring "keep alive signals". If these are not coming fast enough the watchdog kicks in resetting the game. The revision 5 game soft...
Source: http://pinside.com/pinball/forum/topic/system-3-stargate-garbage-dmd-and-beeps-on-boot#post-4169946