How They Work - Double or Nothing - Double Delay Relay
The short version of what this circuit is doing - the double delay relay is sitting powered when you are asked if you want to try for double. If you push the double button, after a short delay the relay loses power. If a win relay hasn't tripped when the double delay relay opens, a missed trip relay is tripped.
Circuit Details
The blue circuit is showing the current path to the double delay relay. The 1-2-3 and 4-5-6 search wiper cam switches are closed when those wipers aren't in the home/locked position, so any time a win is detected those switches should be closed.
The double play relay switch is closed until you push the double button.
The 4th ball relay switch keeps the double delay relay unpowered when the game is reset and the shutter panel is open - except when the start relay switch closes periodically and the double delay relay nonsensically powers.
This circuit was simplified in later games and the double delay relay was powered only by a switch on the double play relay - though in that circuit setup the double delay relay was powered all the time during spin cycling and game play.
That leaves the diode and the capacitor. The 1N4004 diode is a simple power diode. It allows current to flow in one direction only. You can think of a capacitor as a little rechargable battery that also helps smooth out noise/ripples in the current flow.
Since the bingo machine is running on alternating current (AC), the current flow is constantly changing direction... 50-60 times a second. Without the diode in the circuit, current would flow into the capacitor and charge it a little, but when the current changed direction the cap charge would get sucked out again.
The diode will make the cap see a spurt of current, nothing, another spurt, nothing...and the cap will build up a charge. When the double play relay opens, the current is completely cut off and now the double delay relay coil starts sucking current out of the cap (yellow circuit). Eventually the cap will discharge enough that it can't keep the coil happy and the magnetic field in the coil collapses, causing the relay plate to open.
Common Problems/Symptoms
The most common problem is a cap has failed and is preventing the double delay relay coil from powering. The symptom is the missed light turns on as soon as the win is detected, and you never have a chance to push the double button.
These are electrolytic caps, and they'll go bad from age. When replacing the cap, note it has a (+) and a (-) end. Don't put it in backwards, or it will fail quickly and ofter spectacularly.
Much less common is a failure of the diode, and a symptom would be you always lose a double attempt because no delay happens. Pushing the double button immediately opens the double delay relay. There's actually a race condition here. If the double win relay #1 powers and the double win trip relay trips before the double delay relay lets go, you can still win. You should win a double attempt a little less than half the time. If you win much less frequently, you've got a problem.
The diode in Stock Market is a 1N4004. The 1N400x series differs by the reverse breakdown voltage they can handle, but are otherwise interchangeable. The 1N4004 can handle 400V, the 1N4007 is good for 1000V. It may be easier to find 1N4007's, and they can be used instead.
The diode is supposed to conduct current in only one direction. If you put a high enough voltage on the diode "backwards", the diode material will give up and conduct current when it's supposed to be blocking it. The amount of voltage required to force current through is the reverse breakdown voltage.
Although the coil is living in a 50V alternating current (AC) circuit that has been rectified by the diode and smoothed by the capactor into a still choppy direct current (DC) environment, when the power is removed from the coil there is a voltage spike generated by the coil itself as it attempts to maintain the same amount of current flow.
This voltage spike can be quite high, and is the reason a 400V diode - and in later games a 1000V diode - is used. This voltage spike is happening all the time on the rest of the coils in the game, and if the energy released by the collapsing magnetic field in the coil has no place else to go, the usual result is a spark generated in the switch gap.
