The first mechanical slot machine was developed by Charles Fey in 1895. This machine already featured the familiar spinning reels with fruits and card characters. Fey later worked with the Mills company to produce a wider line of machines as they grew in popularity. Jennings, another early slot machine manufacturer, was originally created to refurbish Mills machines. In the 1930s, Bally also began manufacturing slot machines and still does today. Because of similarities in design, the process of repairing old mechanical slots is similar among all brands. Most repair problems originate with a jammed coin in the machine.
Since most repairs require unjamming the machine, do not pull on the large lever. It will probably not fix the jam, and could easily damage irreplaceable parts inside the machine.
Open up the back of the machine by inserting the key into the keyhole and turning. You will now see the machine's gears exposed at the bottom, the reels in the centre, and the bonnet at the top of the machine. The bonnet is a large metal piece covering the escalator, which is the mechanism for accepting coins and moving them into the rest of the machine. Most repair problems come from a jam in the escalator.
Locate the two clasps on the side walls of the machine. These should be roughly parallel to the reels. Pull these clasps up to release them. The bonnet may now be removed. On some machines these clasps may not be on the sides, but directly underneath the bonnet. Inspect around the bonnet for any additional clasps or clips (models differ) and unhook these as well if they exist. Remove the bonnet by lifting up and pulling out, towards yourself.
Examine the escalator, now exposed on the top of the machine, formerly under the bonnet. Find the location at the very top where coins enter the machine. From there, they should fall down a path to a resting place above the reels. If there are any coins stuck along this path, gently loosen them with hands or screwdriver.
Look above the reels, at the bottom of the escalator. There may be a horizontal bar in this location. If you can, insert a coin and pull the main lever on the outside of the machine. Look to see if this action affects the small horizontal bar above the reels. This bar is meant to detect whether a coin is in the escalator, and stop the reels from moving if there is not. On an old machine it could be sticky or stuck.
If the bar is sticky, remove it by unscrewing the screws holding it in place, clean it off, spray with lubrication and screw it back into place.
Re-examine the entire escalator mechanism for sticky levers or gears and jammed coins. The escalator is different on every model of machine, so just look to see if everything is moving properly. If it is, the problem may be elsewhere, and the entire machine will need to be removed from the casing.
Locate the two clasps which connect the mechanical parts of the machine to the base. These are located on the sides, and are different than the clasps which connected the bonnet. Once you've found them, pull the clasps up and out to loosen them.
Grasp the solid bar below the reels, but do not grasp the reels. Pull towards yourself (some machines will need to be pulled up first, then out). If the machine does not come out of the casing, look for a bolt connecting the machine to the base; this is present on some Mills machines. Unscrew this bolt and try pulling the machine towards yourself again.
Examine the mechanical unit very closely with a flashlight, looking for any caught coins. Look at the very bottom, under the reels, everywhere that is visible. Remove the coins with your hands, pliers, or a magnet.
Examine all of the wheels, gears, and other mechanical pieces for sticking. If any are sticking, clean them up with a rag, and spray on some lubricant. If something is stuck, gently push it back and forth with fingers or screwdriver to free up the gears.
Do not force anything that is not working. If possible, contact a professional who is familiar with the inner workings of your particular model and brand.
Watch out for your fingers, as some of these mechanical pieces can exert large amounts of pressure.