Quoted from gweempose:I don't think you necessarily need U1
If you're using an original Bally AS-2518-35 MPU board configured for KISS, you do need U1. Are you replacing a bad one? or Did your board not have a U1 chip installed. I think what gweempose is suggesting is that on the newer boards, you can have your PROMS updated to 2732 EPROM chips which hold twice as much as the original 2716 chips so you don't need U1.
So, if your board had a U1 and you need to replace it, you DO need it for your board to work.
But, if your board didn't have one and you just noticed that U1 is empty, see if the other chips are 2732 EPROMS. If so, you don't need U1.
If you need it, you can download the ROM image from IPDB here http://www.ipdb.org/files/1386/Bally_1979_Kiss_ROMs.zip
Do you have a way to burn a 2716 EPROM? If not, I can send you one for the cost of shipping.
Wow... that was confusing after re-reading it. Good luck.
G