There are many types of pachinko machines and parlor regulations, but most of them conform to a similar style of play. Players buy metal balls, at 4 yen per ball (250 balls for 1000 yen is the current practice), which are then shot into the machine from a ball tray with the purpose of attempting to win more balls. The pachinko machine has a digital slot machine on a large screen in the center of its layout, and the objective here is to get 3 numbers or symbols in a row for a jackpot.

Originally, pachinko machines had a spring-loaded lever for shooting the balls individually, but modern machines use a round “throttle” that merely controls how quickly an electrically fired plunger shoots the balls onto the playfield. The balls then drop through an array of pins. While most balls simply fall through to the bottom of the pachinko layout, occasionally some will fall into the center gate and start up the digital slot machine in the center screen. Every ball that goes into the start-up gate results in one spin of the slot machine, and the maximum amount of “credit” at any given time is 4 spins. This spin credit system is required because it is often the case that a ball will go into the center gate while a spin of the slot machine is still in progress. Each spin typically pays out a minimum of 3 balls, but the ultimate goal is to hit the jackpot and win a lot more. Contrary to popular belief, the program of the digital slot machine decides whether the player has a jackpot or not the moment a ball activates it, not when the numbers or symbols are actually spinning.

During the spinning of the slot machine, when the first 2 numbers or letters of the spin match up the digital program will almost always enter into “reach mode” where many animations and movies are then shown before the final outcome is known just to give the player a boost of added excitement. If the player does manage to get 3 numbers or symbols in a row to obtain a jackpot (average odds of this happening are around 1 in 330), the machine will enter into “payout mode.”

Depending on what type of pachinko machine is being played, the payout mode usually lasts for 15 “rounds.” During each round, amidst more animations and movies playing on the center screen, a large payout gate opens up at the bottom of the machine layout and the player must try to shoot balls into it. Each ball that successfully enters into this gate typically results in around 12 balls being paid out into a separate tray at the bottom of the machine, which can then be placed into a ball bucket for the player to do with as he or she wishes. The average total payout per jackpot is around 1250 balls, or 5000 yen worth.
After the payout mode has ended, the pachinko machine may do one of two things. Almost all of them employ the kakuhen system, which is where half of the possible jackpots on the digital slot machine (usually the odd number combinations like 111, 333, 555, etc.) result in the odds of hitting the next jackpot improving by 10 fold, for instance, from 1 in 330 to 1 in 33. Hence, under the kakuhen system, it is possible for a player to get 3, 10, or even more consecutive jackpots after the first “hard earned” one. Such a streak of jackpots is commonly referred to as being in “fever mode.” If, however, the original jackpot or any subsequent jackpot is not a kakuhen combination, then the machine will enter into “jitan mode.” Here, over the next 100 spins, under the original payout odds a “blossom” opens up near the center gate to make it considerably easier for balls to fall into it. To compensate for the sudden increase in the number of spins over this period, the digital slot machine will produce the final outcomes of each spin much more quickly, typically within 1 second.

Once the jitan mode has ended at 100 spins and no more jackpots have been made, the pachinko machine will revert back to its original setting.

Most current machines include a slot machine component and are known as pachisuro (????, pachisuro?), a portmanteau of “pachinko” and “slot machine”. In pachisuro, big winnings are ultimately paid not from the balls falling into gates but from the slot machine matches that follow. Source: wikipedia.org