Hi, looking for help again on my Hi Dolly.

The Roto target scores correctly, for all numbers, but only pulses the 0-9 unit (with the bell) one less than it should, so 4 times for the 5 target (but adds 5 to score), 3 for 4, etc and none for 1 (again, the score reel moves 1 correctly). This occurs regardless of left or right roto target switch, and regardless of first or second player.

Here's the relevant part of the schematic.

Capture1 (resized).JPG

I have checked all the score motor switches and "appear" good. I figured easiest test is on the 5 target (my red "1" above) as then simply the 1A should fire 5 times (red "2") until 4C Opens (red "3")

But when I manually turn the score motor, with a meter on 1A, I notice that 4C closes just before the final close of 1A. As far as I can see, all the score motor switches are screwed in tight, clean, etc and nothing looks obviously wrong?

Photos of score motor:
Starting position, 4C closed (red arrow)
Capture2 (resized).JPG

Just before motor comes to rest point - 4C opens (red), but 1A firing one last time (blue - the switch is not visible its on lowest row of motor)
Capture4 (resized).JPG

As usual I must be missing something simple/stupid! Ideas?

Well first MarkG thank you for your answer (again) and secondly maybe saving me hours (months) of pain! Your theory is fascinating... and that Gottlieb assumes pinball players would struggle with arithmetic that was target - 1 . Thank you as always.