Why is the search index coil burned out?

Games affected: games between Sea Island and Bounty

The search index coil stops the search wipers when a winner is detected and holds the wiper contacts on the winner while payout is happening. This coil is the most commonly burned out coil in a bingo, and the reason is due to a design flaw.

Like all high power coils, it is not intended to stay powered on for a long period of time. Obviously it needs to be powered for the amount of time needed to complete the maximum payout, and it can handle that, but when it gets stuck on, the coil will get red hot, burning the paper wrapper and eventually the coil wire.

The sequence of operations is supposed to be:

  1. winner is detected
  2. search index coil is activated, holding search wipers on winner
  3. replay cams are released and the control unit motor turns them. The replay cams provide pulses to the replay counters and replay registers to award credits
  4. replay counter reaches payout level, and cuts off power to the search index coil and replay cams index coil.

Sea Island Schem
Timer unit switch shuts off motors
This is fine, except what happens if the control unit motor isn't turning? The search index coil is powered until it cooks. On early bingos, it's not an issue, as the control unit motor is always turning until the game is tilted.

Starting on Sea Island, Bally decided to reduce wear and tear on the mechanisms by shutting down the moving parts shortly after the fifth ball is shot. The timer unit accomplishes this when it reaches it's top step (8th).

The switch at the top of the orange line is normally closed, and powers the motors through the tilt trip switch. If the game tilts, or the timer unit reaches it's top step, the motors stop.

So, it would be a bad idea for the motors to stop during payout. The obvious way to stop this from happening is to make sure the timer unit can't step up while payout is occuring. Let's see what Bally did.

Sea Island Schem
Timer unit stepup circuit
Hmmm...looks like the timer unit can step up a couple ways. The orange path is the one we care about...the other branch through the ball lifter cam is what is counting the first five balls played so the selector lock trip relays can be tripped. CU cam 1A and the drag arm switch closing at the same time provide the pulse to the stepup coil. CU cam 14B, according to the manual, is there to break the circuit to the stepup coil while payout is occuring. Unfortunately, CU14B is on the same set of cams as the replay cams, so it must turn while the payout is happening. If you happen to get the 1A and drag switches closed at the same time as the CU14B cam lobe is at the top (closing CU14B), the timer unit will step up.

The addition of CU14B makes it less likely for the timer unit to step up, as you need three things to happen at the same time instead of two, but it's still possible for a pulse to sneak through.

So it becomes an intermittent race condition. If you happen to push the 'R' button to start the payout when CU1A is closed, then CU1A and CU14B will open/close together. When all three switches close enough times, the timer unit steps up and the motors shut off while the search index coil is still powered. You'll need a larger payout for this to happen.

If the player is standing at the machine and it shuts down while payout is happening, pushing the 'R' button resets the timer unit, the motors start again, and payout continues. If the player walks away....trouble!

On Bounty, Bally added another path on the motor power circuit which went through a switch on the replay cams index unit. This circuit kept power on the motors while the replay cams index coil was powered, but had the disadvantage of adding another 120V circuit to the game.

At some point after Bounty, probably on Border Beauty, Bally decided the extra 120V circuit was daft, and they just moved the CU14B switch to the replay cams index unit, which effectively stops the timer unit stepup while payout is happening.

Possible Fixes

There are a few things you can do to fix this problem:
  1. do nothing...just don't leave the game if you get a big payout until the payout finishes

  2. if you have the spare parts, add another switch on the replay cams index unit and move the two wires from CU14B to it. The switch should be adjusted to close only when the replay cams are locked.

  3. disable CU 1A by bending up the switch blade so it can't ever close. Doing this means the timer unit never steps up far enough to turn off the motors, so if you leave the game on when not playing, this is not a good option.

  4. and another fix from alan (who has machines for sale): Add an extra switch to the stack at the search wiper (where the feed ring & R button index coil are located) use the 110v circuit for the control motor, thus not allowing the control motor to stop running unless the search wiper is back to Zero position.

  5. Jeffrey Lawton recommends moving switch 1A wires over to a new switch on the search wiper stack (if the game has one). See Jeffrey's writeup of this problem. This is maybe better than alan's soluton, as it does not require an extra 110V switched circuit.

  6. An operator in Reno probably did the most thorough solution. He added an extra relay to the game and ran 14B and all the switches currently on the search index unit through the switches on the new relay. He removed all the switches from the search index unit except on, which was used to close the new relay. This helped prevent the fibre tab on the search index unit that was lifting all the switches from bending/breaking due to having to lift up multiple sets of switches.