disconnect the Credit display - still happens ?
Then ;
disconnect the battery for 15 minutes - Fire it up without the battery.
Could be a dodgy CMOS 5101.
straight from the Marvin's guide (thought I'd seen this before !)
"Player one display always displays the same information that's in the credit/ball display."
Maybe a problem with the start button! The start button has a piece of "fish paper" (insulating paper) behind the last leaf. This stops the switch leaf from touching the metal support behind the switch. The fish paper had torn, and allowed the switch blade to touch the metal (grounded) support. This has the effect of grounding a row or column of the switch matrix. This will cause all kinds of strange problems! A new piece of fish paper, and the player one display worked fine.