For this answer, we turned to our deep-throat casino manager Arnie Rothstein, who deals with the paperwork generated by this very question for hours every day. Take it, Arn.
A slot machine’s EPROM (erasable programmable read only memory) chip is preinstalled when it’s manufactured at the slot machine factory. The customer (the purchasing casino) has numerous options to choose from that pertain to the "hit frequency" (how often a winning combination comes up on the machine) and "payback amount" (the percentage of coin-in that the machine returns to the player).
All machines come from the manufacturer with a "PC sheet." The slot maker prepares the sheet, which contains information about the make, model, pay table, amount of pay stops, frequency of hits, reel strips, theoretical hold, and other data on the machine.
Most casino jurisdictions require that the casino maintain a PC sheet for every slot on the floor. Nevada casinos are required to make frequent slot audits, which the Gaming Control Board reviews at will. (All casinos and gaming manufacturers and suppliers are audited by their respective control agencies.) Casinos regulate their machines and investigate any machine that deviates from a certain range of expectation, also known as a Volatility Index. (To calculate a slot machine’s VI is a long drawn-out mathematical process, but it’s accurate to within thousandths of a percentage point.)
Some casinos have the technical ability to reproduce a damaged EPROM chip. But these chips must have Gaming Control approval, since all EPROMS have serial numbers and long paper trails.
You can see evidence of how involved the EPROM process is when a major jackpot is hit.
Let’s say I’m your lucky charm and after reading this, you go out and line up three Megabucks symbols. You’ll immediately see the floor come to life. Security guards and floor people will watch the machine. Slot techs, a member of the slot manufacturer’s team, and a surveillance agent will be present to see the machine being opened. The EPROM will be tested by both the house and surveillance and the serial number verified. Then, and only then, will you be paid.
So, turning to your question about slot machine chips that disallow the big jackpot. Can this happen? Sure it can.
In the good old free-wheeling days, when casinos were far less regulated and some took advantage of that, slot techs had all kinds of tricks to prevent the big jackpot from being hit. For example, they used to spot weld the reel tabs so the mechanical fingers couldn’t slide into the reel that completed the big-jackpot combination. Then there was the Gaming tech who fixed a machine to pay when a certain sequence of buttons was pushed.
Even then, though, it wasn't so much the casinos that tried to gaff the machines not to pay off as it was the slot thieves who tried to gaff the machines to pay. One gang opened the machines and replaced the EPROMS right under the surveillance department’s nose; the gang figured out that surveillance didn’t have the right equipment to videotape that area of the casino.
Of course, as casinos are watched more closely, slots get more sophisticated, and surveillance gets more efficient, such incidents have become increasingly rare. But that doesn’t mean it’ll never happen again. Somewhere ... someone ... is working on a plan.
