On the playfield there are two targets of 1000 points each, a switch of 500 (when lit 5000) points and a kick hole of 3000 (when lit 5000) points. When the ball hits one of these targets sometimes the score is NOT counting (0 points) or 1000 points (regardless which target) or counting according the specified points (correct). Note: when the switch is at his 500-position (so beneath the 1000 points) the score is added correctly.

On the other side the points are added correctly by the score reels. For example when hitting a mushroom of 100 points 11 times in a row, a score of 1100 points is added. If followed by a triple hit of lets say 500 points each, the pin added 1500 points and the score reels are rotating accordingly to these points. So the score reels are working in the right way.

So only when hitting targets of 1000 points or more, sometimes a score is not added at all or with the wrong points.

Can someone give me a hint where to start checking?