The not-happening is what makes the games gambling devices in many jurisdictions. Generally, something would improve initially as each coin/credit was played, but as the scores/features got better, it became more likely that cycling the machine flashes the lights but nothing else happens.

Many games also have a third/fourth card which explained unique features of the game, or indicated the OK game/red letter game guaranteed minimums.

About the most frustrating thing to do when playing a bingo is drop a ball in a hole that is already spotted, thus wasting the ball.

The one-way metal flap at the top of the ball runway which the ball passes under to enter the main playfield area.

Besides preventing the ball from re-entering the runway, there's a switch under the metal shell that triggers the lifter start relay to turn on the ball lift motor to raise another ball...unless you have one of the few games with a manual ball lift.

Manual

A plunger below the ball shooter can be pushed in at any time to raise a ball for play.

Automatic

A motor raises the ball when appropriate. On most games, a ball is raised as soon as the current ball leaves the ball gate. Some later games actually detect when a ball has fallen into a hole, and raise the next ball then.

The rubber tip should be replaced if torn, as pitted balls will damage the playfield quickly. The rubber tip and springs are cheap and and easy to get.

Between the clutch plate and the thing you want to turn or hold still is an oil-impregnated leather washer. This washer is what slips. The surface between the washer and clutch plate and/or the washer and thing to turn may be the part that is slipping.

You're supposed to oil the washers with neatsfoot oil occasionally, but for limited use games occasionally = years. For games that have been sitting a long time, the clutch washers are often stuck and the only good solution is to disassemble the shaft to free and reoil them.

The pic shows a couple ok washers as well as some worn/damaged ones.

The condition of this door can tell you a lot about how the game was operated. If the coin door has extra metal, locking bars, or gouges from attempts to pry it open, the machine has had a hard life.

In this pic, the arms are highlighted. The right arm is missing the drag arm stop. See dram arm stops.

Some very late model bingos didn't use jones plugs. They used plastic amphenol connectors instead.

From a players point of view, proportioning simply means that the higher your scores/features go, the less likely it is that the game will give you extra balls or increase the scores/features even more.

The sliding board under the playfield that allows/prevents the balls from dropping through the holes is the shutter panel.

On most games, a metal bar is attached to the shutter panel and it pushes a set of switches when the shutter is closed. On the schematic, these switches are called "panel switches" or "shutter switches".

It's not unusual for the bar to loosen and not operate the switches correctly.

On some games, the panel switches are called shutter switches and you see things like "shutter sw. closed when open". While this is probably a more correct term ("panel" was also used for the flip-down board in the head that had all the lamps on it), it's also confusing because the shutter motor cam switches were sometimes labelled something a bit shorter than that - like "shutter cam 3C" or "shutter motor 3C". The almost always safe thing is to look and see if the switch in on the shutter cams by looking at shutter motor diagram in the manual for a switch with the right wire id's connected. If you don't find it there, and you aren't unfortunate enough to have a manual with a lot of errors or no shutter motor diagram, look on the bottom of the playfield at the panel switches.

On games where you could rearrange winning combinations via things like the magic screen, you need to push the R-button for every winning combination you set. If you don't find all the possible winners before starting the next game...too bad!

The main reason for the R-button was to have more control over when scoring happened, and it had the nice side effect of reducing wear in the game, as the search disc was held stationary until the R-button was pushed.

On earlier games where the search disc was rotating constantly, the contacts on the search disc and the search relays would wear away.

As it stepped up/down, electrical circuits in the game were broken/made. The circuits were used when playing for increasing the scores/features or extra balls.

Bally marketing speak referred to the reflex unit as "proportioning the game". What that really mean is that as credits are awarded, the game is less likely to give you extra balls or increase the scores/features.

As credits are played off/coins deposited, the game gets more generous.
The reflex unit does not reset between games, so if you win big, leave the game and let someone else loosen it up with their money!

See reflex unit

In early games, there is one of these units. If, for example, you win 12 credits for a 3-in-line, the counter will step up as the credits are added to the replay register. When the counter reaches the 12-level, payout stops. If you then pot another ball to give you a 4-in-line, the counter starts stepping up from where it left off until you reach the 4-in-line level.

Later games have multiple replay counters, so they can pay wins independently. For example, games with triple deck advancing odds/scores have three replay counters, one each for the red/yellow/green winners.

see also: score disc/replay counter

As the scores advance, the chances of lighting additional features reduces.

see also: score disc/replay counter

As the unit operates, it closes the search relays when balls are in the particular holes it is looking at. If the correct number of search relays are closed, the search stops and payout circuits are activated.

After payout completes, the search continues for more paying combinations. Higher payouts can actually get broken into two pieces - payout for a 3-in-line, a pause, then the remainder of the payout for a 4-in-line or higher.

see also: search disc techno details.

It's the search relays that make all the clicking noises heard on the early bingo's.

The amount of clicks increase as more balls are in playfield holes.

see also: search disc

The shutter panel normally closes when the first ball opens the ball gate switch on a completely reset machine. Complete reset of the machine requires all balls to be in the ball trough, so if you power off a game with a ball in the ball runway, then power on and start a game, shooting the first ball will not close the shutter. Once all the balls are beneath the playfield, reset is complete and shooting the next ball will close the shutter.

Some of the wiper/contact plate assemblies like on the spotting and search units have wipers that spin in one direction only. Since they don't step up a limited number of times and reset like the wiper/contact plate assemblies on stepper units, it's not possible to connect wires to the wipers themselves - they'd twist up and tear off.

The solution is to use rigid wire wipers riding on the edge of copper discs in grooves on the unit wiper hub. This creates a little confusion in the terminology:

1. wipers / unit wipers - e.g. search wipers - these are the ones that are running around the contact plate connecting to rivets.
2. slip rings - the grooved channels on the above wiper hub assembly
3. slip ring wipers - the rigid wires connecting the hub to wiring. These wipers should have a slight flex to apply pressure to the slip rings, but excessive pressure will wear the cupped section off the slip ring wiper a lot faster.

see stepping units