Our subject for this edition of Tech Tips is coin doors, and certain related issues that an arcade game owner may experience in the operation of a coin-operated device.

Note: The following article deals with American-style coin doors and mechanisms. While many of the concepts here can be applied to Japanese and European-style doors, the latter may have some different features (such as using Electronic Coin Comparators or radically different setups in getting the coin from insert-to-bucket) and can require a different approach to repairing them.

Diving Into The Coin Door

The coin door is a basic, and essential component found in coin-operated/pay-to-play amusement games. If a game has no coin door, then it has been designed to be free play.

Since this is the gateway for you or your customer to be able to pay for the game, it needs to be functioning properly. If it doesn’t, then a machine won’t play, which results in frustrated customers and lower earning games.

Here is a diagram of a coin door from both sides to help you identify essential pieces in such a door. This was taken from a Raw Thrills game and is typical of a two-slot coin door found on many machines. With more locations switching over to card swipe systems, those will often remove the coin slots and only feature the card swipe reader. Such readers are very different in how they work and will not be covered in this piece. Click on the image below for a larger/closer view:

Breaking It All Down – What Does What?

Based on that image above, here are more details on those terms:

Coin Slot: Where the coin is inserted. Most slots are designed to accept coins a little larger than a quarter. If you have a machine from the 1970’s or 80’s, it is often possible that it will not accept anything larger than a quarter. If that is the case, then the slot has to physically widened using moderate force (using a small chisel or screwdriver and a hammer)

Does it matter which coin slot I put the coin into? Usually no, but sometimes it does. This is answered in more detail by our friends over at Arcade Heroes.

Coin Reject Button & Slots: A spring-loaded button, usually red, but sometimes yellow or orange, that when pushed, opens up the Coin Mech inside to cause any coins jammed within the mechanism to fall into the coin reject slots below.  These are lit from a small incandescent or LED light from behind (Coin reject backlights).

If you insert a coin and nothing happens, then there is likely a jam.

• Push the button in, and a coin or two should fall into the reject slots/boxes at the bottom. If nothing falls, then the jam may be a little more serious and needs an attendant to look at.
• Sometimes several dollars worth of coins can be jammed into the sloped lane, so they will not drop. If you come across such a jam, you will probably need something like a flat head screwdriver and push the coins out while removing the coin mech (or holding it open).

The outer plastic (sometimes metal) form of the coin slot is held in place using small screws found on the inside of the coin door. If you need to access the coin reject buttons, remove these screws and pull off the form. This is also how you can change out the Coin Inserts (not pictured, but these are the small thin strips of printed plastic that will typically say 25¢ || Push To Reject) if you wish.

Lock: Self-explanatory in it’s function. If a lock isn’t working, it can be a couple of issues.

• If the key turns and nothing happens, check and see if the large screw at the back of the lock is tight (but not too tight – sometimes that prevents the keys from turning at all). These usually work with either flat-head or Philips-style screwdrivers.
• If the door is loose(it closes but may open slightly by itself), opens easily or the lock will not close when you turn the key, then this is an issue with the lock latch. If the screw at the back is sufficiently tight, then the angle of the lock latch may be wrong for what the cabinet needs. Try removing the screw, then flip the lock latch around. If that still doesn’t solve it, then you may need to bend the latch using pliers. If the door is loose, bend it a little until secure. If the lock is not closing and flipping the latch around didn’t work, then bend it enough that allows the lock to close properly.
• If the lock is loose, then the large nut that is supposed to hold the whole lock in place is not tight enough. Just tighten it with a wrench.
• If a key breaks inside of the lock, then the only way to get into the door will be to drill out the lock. Just be mindful of the force you use with any key/lock; you shouldn’t have to apply much pressure to turn the key, so if it’s being difficult, don’t ramp up the pressure, otherwise you’ll probably break the key.

Dollar Bill Acceptor: Often abbreviated as DBA, these are also known as Dollar Bill Validators (DBV). The latter term is usually used in vending applications. Most coin doors and modern games have a cut out for DBA’s and internal wiring to work with major DBA brands; on rare occasion a game will ship with the factory with one installed. Bills go into the Bill Stacker, a spring loaded box at the back. The larger that these

We’ll just cover the basics on these, as there is often much more than can be done in that regard than the scope of this article. Consider it to be a subject for a future Tech Tips!

• Not accepting a certain bill? First make sure that the acceptor has proper labelling on it. Some bill acceptors will only accept $1’s; some are made to take only $1’s & $5’s; others up to $20; but also the operator can adjust an acceptor or the game machine to only take certain bills, even though it might be capable of taking other values. $2 bills are one example – some DBA’s will accept them, but the operator can turn that feature off.
• If a DBA isn’t taking a bill that it should be accepting, it can come down to the condition of the bill itself. Bills that are severely crumpled, ripped or torn can become jammed inside of the mechanism. Bills marked with ink or stamps may also be rejected. If the acceptor regularly rejects legitimate bills, then some may have a tiny switch that changes between high security or high acceptance; choose the latter and it can work better.
• If you are still having problems, then the acceptor might be dirty, or another bill (sometimes a coin or even a credit card) might be jammed inside. There are third-party cleaning tools available for DBA’s that you can purchase and use to keep them clean and working.
• If some other issue is taking place with the DBA, and it is powering up, then many have a diagnostic mode or tell you what is wrong by blinking a certain number of times. You will have to find and refer to the DBA model’s manual to determine what the error may be depending on the number of blinks; often this information is also published on a sticker placed on the bill stacker of the unit.
• There are more advanced troubleshooting techniques to consider (voltages, pulses) which will be saved for a future, more expansive article

Coin Mechanism (coin mech): When a user inserts a coin into a machine, it passes down the coin guidance lane and then enters into the coin mechanism. This is a rectangular component that is used to determine if the coin entering the machine is the correct one wanted for acceptance. Usually just called coin mechs, their main purpose is to size and weigh the coin, letting it pass through to the coin switch and then coin bucket if legitimate or the coin reject slot if incorrect. Here is what the process looks like in slow motion:

There are many different brands of coin mechs that you can find, with Suzo Happ/CoinCo, Coin Mechanisms and Imonex being the most common and popular. These are also designed to accept one type of coin by default, so when shopping for them you may seen them called a “25¢ coin mech” or “.984 token mech.” Often they can be manually adjusted to take other types of coins.

Most coin mechs have 4 tiny cylinder shaped screws that are used to hold the mech in place in conjunction with the coin mech brackets and bolts. Some coin door styles will NOT allow you to insert a mech with all four screws in place; you may have to remove the two that are on the side of the door itself to fit the whole thing in place.

There are larger screw-in bolts seen in the diagram at the top which are used for holding mechanisms in place. If these bolts become loose, or the brackets fall out, then this will cause a misalignment of the mechanism which leads to a coin jam. Ensure that the bolts are tight and brackets are in place. If you constantly have issues with alignment, you can take a couple of zipties and wrap them around the bolts to tighten this all into place.

For a deeper dive into coin mechs, we’ll share this useful explanation video produced by Coin Mechanisms (CM), which covers what you would need to know in case a coin is not falling through correctly:

Coin Switch: After the coin passes through the coin mechanism and is accepted, it then drops through a slot to activate the coin switch. The coin switch is a large microswitch that has a long, spring-loaded wire arm attached to it. The coin pushed the arm, making a an electrical connection and completing the circuit inside of the switch. 5V Electricity is provided by the coin switch input and ground wires that are a part of the wiring harness. These wires are assigned by the I/O of the game to tell the game which switch is being activated. Note that coin switches are not universal in their design, with different brands and styles used on some older games where the metal arm has a different placement or reach. While the general operation is the same, keep this in mind that you’ll want to replace the switch with the same kind if possible. Sometimes the coin door you will be using also uses a specific molding made for a certain switch; the examples above use a vertically placed switch, but many games from the 80’s and 90’s used varieties of  horizontal-set switches.

• If the coin switch does not activate, then there may be a fault with the wiring. Check the input and ground wires; First make sure that the wires are connected to the metal leaves of the switch; the ground wire always connects to the bottom-most leaf. There are two possible input leaves, and the input wire generally connects to the leaf furthest away from the ground. It’s normal for one of them to have nothing connected to the leaf in the middle (as seen in the diagram at the top.
• If connections check out, then it might be the wire itself. Inspect the wire and connection to ensure that there is a proper, uninterrupted connection to the game I/O (this can be checked using a voltimeter). If the wires are ok, but the switch isn’t responding, try replacing the switch.
• If a coin is getting stuck at this point, it is often the fault of the wire arm. If that is bent out of place, it needs to be straight. This can be fairly difficult to set correctly, and may require various attempts to get it right. If you have no success, the easy solution is to replace the switch with a new one.
• If a coin mech is older and dirty, there is no harm in placing these into the top rack of a dishwasher to clean them. You can also hand clean them using soap and warm water.

Note that the larger green/yellow grounding wire that is often found inside of doors is a more generalized ground. If there are a number of hard-to-track down issues with the door, or static discharges when people touch the door, ensure that this wire is properly connected and grounded.

For one item that is not shown in the diagram above is a slam switch. This uses two or three long metal strips with a weight on one end. This switch is used in some coin door designs to prevent users from pounding on the door to trigger sensitive or poorly wired coin switches into providing free credits. It is common to find this on older doors; newer coin switches have been designed to be sturdy enough to prevent the need for such a switch.

Often when you open a coin door, you will see a small set of keys hanging on a hook. These are keys for accessing the back of the game cabinet (such as the monitor or computer hardware).

That covers the essentials of arcade coin doors. If you’ve missed our other tech tips articles, then be sure to check them out here!

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