I could use some help on this problem as I have spent considerable time trying to figure this out to no avail over the past 2 weekends

I have had the above bowler for over 5 years and this past year a problem has crept in:

Randomly, or so it would seem, the machine will skip a frame forward to next player.
The machine functions perfectly well otherwise
It normally tallies strikes and spares appropriately
the offending behavior occurs in single player or multiplayer modes
it seems to occur only after the first ball is thrown for a player

For instance if it occurred on the second player of a 4 player game, the second player would bowl, pins would go up and then then it would jump to the third players turn. the pins would not reset and the third player would get one ball to play before it would change to the 4th player up and score whatever was the combination of the second players throw and the third players throw

If in the above instance the second player had a spare the prior frame, after the first bowl it would start scoring in the second persons position immediately after the roll but often finish scoring pins on the third players bowl inappropriately after it skipped

If one is bowling in a one player game, it would just skip a frame forward.

My return switches all seem to be functional and not sticky. Everything else seems to be working well

I do not have the schematic unfortunately but do have the manual which I have tried to use to no avail

does anyone have any ideas on what to look at. since the behavior seem to be random, I have not ideas at present.

It is a bowler, 3 inch balls

Yes a schematic would be great but I have been unable to find one.

I will check the score control relay and get back to you, i had already checked the gaps and thought them to be ok but will recheck and will check the extra shot reset (did not think to check that one)

On Pinball RGP it was suggested to check the travel on the steppers as they might be over plunging possibly, I have checked most of the relevant ones but have yet to eliminate the behavior. It happens only about once a match, if I cant fix it it may be a new element of gameplay at my house

Thank you so much for the help!

Hold your breath but I just got through a 4 player game and 2 player game without it happening. I re-looked at the switches you suggested and also went through the switch stack/ steppers and made certain none of the tabs were close to each other in the event the shake and rattle of the bowler was potentially creating a short. Your responses and some others i got made me think about things and realize it has to be something like a loose switch or relay. I’ll follow up if the problems returns

i may take you up on the bowler schematic. Let me look through some schematics I have in boxes I unfortunately inherited recently from a friend who was in the Biz for 60 years and see if I have something analogous to what you may have. I started out with pinball but these bowlers are amazing. I imagine one day when I retire I may give it a good refurbishing.