Good advice from several sources here!
Does the MPU board exhibit alkaline corrosion damage? System 11 games suffer heavily when such damage is present.
Here's a pic of a System 11 board with alkaline damage that has leached under the solder mask. The darker colored parts of traces are alkaline damage. Eventually, this will eat completely through the trace, severing connectivity.
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Chris Hibler - CARGPB #31
htp://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The Place to go for Pinball Repair Info