Do you know when the bell is suppose to sound? on all pays or just jackpot?
that was one of the differences between the various 809 models. Different customers wanted more or less noise.
you have a common problem ... your model/serial number plate says 809-N, but you have a service button on the door. The 809-N did not have a service button (according to the schematic). You could have anything from a replacement door bezel to it being a different machine with the serial number plate swapped on.
the service button would just turn on a lamp on the light tower poking up from the top of the machine. If your door button is wired, look at the wire colors and look for a terminal block in the top compartment where the wires from the tower attach. See if you can figure out the wiring based on the colors, or if necessary use a meter to verify.
an 809-N rang the bell on a 777 or whenever the bar jackpot relay powers. The bar jackpot relay powers when you have three matching bar symbols.
the bell actually would stay ringing as long as the reels stayed on matching symbols, so if the player walked away, eventually I assume someone had to come by and shoot the machine to shut it up ... or at least drop in a coin to disconnect the pay circuit.
most machines would only ring the bell for the duration of the payout for non-jackpot wins - it would be easy to change the behavior of the 809-N to that mode by changing a wire on a bar jackpot relay switch.
you can test the circuits with jumper wires or a voltmeter. Have a preference? You usually need a couple jumper wires (alligator clip test leads) when using the meter since you often want to check voltages with the units inside the machine, so clipping the lead onto something and hanging the other end out the front to attach to the meter is the easiest way to check voltages.