Williams WMS Dotmation 40x reel slot machine Model 401

[bullwinkle043]

Looking for percentage chip

[playklax01]

Not sure what chip that pic is of, but to change the percentage on these machines you just need a different XU-3 (or XU-2, it's been a while) chip.  Also would need a clear chip since you're changing the game.

[bullwinkle043]

the machine has been confirmed to be a model 401 Williams WMS Dotmation 40x reel slot machine

[bullwinkle043]

The Jackpot Party percentage chip model 401 refers to a specific model of Williams video slot machines. To change the percentage chip settings on this model, you need to remove the CPU board from the card cage, insert the chip into the XU-27 socket, and then power up the machine. After that, you can select the desired percentage setting for the game.

[playklax01]

I think you may be reading the instructions for a 550 machine.  400/401 machines have 2 EPROMS for the game in XU-2 and XU-3.  Those 2 chips control the theme and percentage.  The other chips that would/could be changed are XU-17/18/30/31, but those would only be for the sound.  XU-27 is a socket for a security PIC.  Typically it is not populated, I've had many machines and never had anything in that socket.  The chip you posted a picture of looks like one that goes in XU-28, but that would not be of any typical concern nor would it affect the percentage (in other words, don't touch that chip!). 

Video machines have a menu that may allow you to choose from differing percent paybacks, if they're available.  However, these mechanical machines have 1 payback percentage programmed per EPROM set.  There is no menu, and you cannot just select or change which amount you want.  There may be people out there (or on here) who have a vast library of Williams EPROMs and can hook you up with what you're looking for.  The payback is hardwired into the chips, and you'll need to change the chips to change the percentage. 

With that, as I mentioned earlier, you'll also need a Clear Chip if you don't have one.  If you change an EPROM, the machine will require you to insert the Clear Chip to reset the game and accept the new chip you desire.  So don't do this unless you have both the new EPROMs and the Clear Chip, otherwise you'll temporarily brick your game until you have both things.  Clear Chips are still readily available (eBay again).