I had a similar problem on my Super Star.
Turns out it was kinda by design. Options were to have a coin start the game immediately (and not increment the credit wheel) or to have one coin add x credits (where x is between two and... seven, I think). No option for one coin, one credit.
In the end, I installed a new wire from the coin switch to the credit wheel increment solenoid, with a connector in the headbox (so I could take the head off without having to desolder my patch wire!).