Bally 873 - sometimes starts back to 1st coin when adding 5 to play

[Chedderboy]

I have a Bally 873 EM that I bought a few months back.  Since times are tight now, I haven't taken it to be fully shopped.  I am wondering if this is something I may be able to fix?  When you are adding coins to play (5 line machine), sometimes when adding a coin it will go back to the first pay line, making you start over adding coins to play the full five lines.

Any ideas?

[Op-Bell]

Take a close look at the coin step-up unit in the top. It has a spring loaded ratchet wheel. Each coin pulls in a solenoid to advance it one step, and there's a floating pawl to stop it spinning backwards. The reset solenoid lifts that pawl to reset it on the first coin. If the pawl pivot is sticky or the spring is weak or missing, it may stay up away from the teeth after it lifts to let the ratchet advance, so it spins back when the step-up solenoid releases. It's all greasy around there so a good clean may be what it needs.