You must have zero credits on the machine before you begin.
Turn off your machine, and pull out the tray that holds the MPU board (located below the monitor). You just have to grab the metal handle and pull the tray towards you. Be careful not to generate static electricity as you handle the board.
Over on the left side of the board is a base eprom. You must remove this base chip, be very careful as the legs of the chip are very easy to bend or break. I use a small screwdriver with the end bent at almost a 90 degree angle. I slowly work the chip up from either end until it is out. Also, one end of the chip has a little notch in it. Note the position of the notch as everything must be inserted in the same direction. The board is also imprinted in white showing the position of the notch.
Now insert the key22 where the base chip was with the little notch in the same position as the base chip. Be sure every leg of the chip is fully inserted into the board. Now put the board and tray back into the machine and turn it on. A screen will pop up with three choices. The first two are for clearing the machine, the third is for "keychip after reboot". You want to choose the third choice only. You navigate the screen using the little white service button on the board and select your choice by turning the jackpot key. Below the three choices it says something like "reboot machine" (I don't remember exact wording) and you turn the jackpot key again. It will then tell you to replace your base eprom and power the machine down.
Remove the MPU board again after you shut off the power and remove the key22. Once again, be careful. Now put the base chip back in and be sure the notch is in the correct position. Put the MPU back in the machine and turn it on. Once it boots up you should now be in the keychip menu and can make your game selections etc. Once you exit the keychip menu you cannot go back without doing the whole process over again so be sure you have made (and saved!) all the selections you want to do.