I have a 1090-10 $1 3 reel 3 coin Bally Machine. My problem was a burnt coil on the Step Up Coil Assembly.
I had problems with my machine advancing the coin input. It was a bad coil up top. There are relays behind the upper glass and lamp assembly. There is a coil that, when energized, will advance a wheel and when it gets to the 3rd coin it is reset by another coil. That coil is closest to the center of the machine and right in your face. It stokes when the coin wire is triggered. when it hits your max, it causes the lower coil, on the Step Up Unit Assembly, to stroke and reset. Initially with the power off play with it and see what it does. Then you can put power to it and with the glass off and the lamp assembly tilted forward, watch and see where it hangs up. you can check my posts and see what I said was going on and the fix.
I believe that once you fix this it will unlock the coil and allow the coins to fall into the hopper...
The switch that is on the side of the machine, under the pivot point of the arm, is used to reset when a big jackpot is reached. The key resets it. A forum member, Amechanic, told me that operating the coin drop wire with the door open will reset that when you pull the arm. I don't have the key for my switch, so that will be what I have to do.
Good Luck...