You can't purchase a new PROM, you could look for a used one but that doesn't make sense because you can just mod the board and burn an EPROM. But first, you have to determine if that MPU is a -17 or -35. NR takes a -17 board.

Second, you will have to modify the board you use to accept EPROMs because PROMs are no longer made.

Third, you will have to check jumpers on the MPU. If they are not correctly set, the board will NEVER boot.

So, back to your question. Even though the U2(E-724-25-U2) PROM is not correct, your game should still boot and start a game just fine.

IF IT DOESN'T, it's broken in another way. Could be power related, could be MPU related.

The different roms in a Bally -17/-35 game only essentially control what lamps and switches do what in the game. For testing purposes, you can put any roms in U2 and U6.

Below is a chart of PROMs for reference. But, if you don't have one, you will be forced to mod your MPU to take EPROMs.

You are probably sorry you asked now... Unfortunaltely SS pinball repairs are most often NOT a "just do this, and then it works" scenario.

Bally Pinball CPU Board ROM Numbers, sorted by ROM number.
On the top of every 1977 to 1985 Bally pinball black masked ROM there is a part number. The list below shows what pinball game this ROM part number goes to on the CPU board.

ROM # : Game Used In
------- ------------
E720-07 : U6 for Freedom.
E720-20 : U6 for Strikes and Spares, Eight Ball, Night Rider,
Black Jack, Evel Knievel, Mata Hari, Power Play.
E720-21 : U6 for ?
E720-28 : U6 for Lost World.
E720-30 : U6 for Playboy, SMDM, Super Sonic, KISS, Eight Ball,
Strikes and Spares, Paragon, Voltan.
E720-34 : U6 for Harlem Globetrotters (-35 only; Use with E750-7 & E750-8)
E720-35 : U6 for Dolly, Future Spa, Globetrotters, Groundshaker, Hot Doggin,
Mystic, Rolling Stones, Silverball, Space Invaders, Viking.
E720-37 : U6 substitute for Space Invaders
E720-40 : U6 (9332) for Frontier, Skateball, Xenon.
E720-52 : U6 (9332) for EBD, Embryon, Fireball II.
E720-53 : U6 for BMX, Centaur, Electra, Fathom, Mr & Mrs Pac-Man,
Speak Easy, Spectrum, Vector.
E721-21 : Night Rider U1 2716 combo (Use w/E720-20 U6)
E722-17 : Evel Knievel U2
E723-14 : Eight Ball U1 (set 1)
E723-15 : Eight Ball U2 (set 1)
E723-16 : Eight Ball U4 (set 1)
E723-17 : Eight Ball U2 (solo w/U6)
E723-18 : Eight Ball U1 (set 2- use w/E723-16 U4)
E723-19 : Eight Ball U2 (set 2- use w/E723-16 U4)
E723-20 : Eight Ball U2 2716 combo (use w/E720-20 U6)
E724-25 : Power Play U2
E725-21 : Mata Hari U2
E728-32 : Blackjack U2
E729-18 : Sound ROM: KISS, SMDM, Lost World, Playboy, Super Sonic, Star Trek
E729-51 : Sound ROM: Dolly Parton, Paragon, Globetrotters, (others?)
E740-16 : Strikes & Spares U2 (use w/E720-20 U6)
E741-10 : Super Sonic U1
E741-08 : Super Sonic U2
E742-20 : SMDM U1
E742-18 : SMDM U2
E743-9 : Playboy U1
E743-10 : Playboy U2
E743-13 : Playboy U1 (opt 1- use with E743-10 U2)
E743-11 : Playboy U1 (opt 2)
E743-12 : Playboy U2 (opt 2)
E743-14 : Playboy U1 (opt 3- use with E743-12 U2)
E743-30 : Playboy U6
E744-03 : Voltan U1
E744-04 : Voltan U2
E745-11 : Star Trek U1
E745-12 : Star Trek U2
E746-11 : KISS U1
E746-14 : KISS U2
E748-15 : Paragon U2
E748-17 : Paragon U1
E750-3 : Harlem Globetrotters U1
E750-4 : Harlem Globetrotters U2
E750-5 : Harlem Globetrotters U1 (-35 only)
E750-6 : Harlem Globetrotters U2 (-35 only)
E750-7 : Harlem Globetrotters U1 (optional)
E750-8 : Harlem Globetrotters U2 (opt)
E776-8 : Nitro Groundshaker U1 (-35 only)
E776-9 : Nitro Groundshaker U2 (-35 only)
E776-10 : Nitro Groundshaker U1
E776-11 : Nitro Groundshaker U2
E776-14 : Nitro Groundshaker U4 Sound
E776-15 : Nitro Groundshaker U4 Sound (opt)
E776-17 : Nitro Groundshaker U1 substitute
E777-8 : Dolly Parton U1 (-35 only)
E777-9 : Dolly Parton U2 (-35 only)
E777-10 : Dolly Parton U1
E777-11 : Dolly Parton U2
E777-12 : Dolly Parton U2 (-35 only)
E777-13 : Dolly Parton U2 (opt)
E781-2 : Future Spa U4 Sound
E781-5 : Future Spa U4 Sound (opt)
E781-6 : Future Spa U1 (-35 only)
E781-7 : Future Spa U1
E781-8 : Future Spa U2 (-35 only)
E781-9 : Future Spa U2
E786-8 : Silverball Mania U4 Sound
E786-11 : Silverball Mania U4 Sound (This may be confused with a U1 MPU chip)
E786-14 : Silverball Mania U1 (-35 only)
E786-15 : Silverball Mania U6 (-35 only)
E786-16 : Silverball Mania U1 (-35 only- use w/E786-17 U2)
E786-17 : Silverball Mania U2
E792-2 : Space Invaders U4 Sound
E792-7 : Space Invaders U4 Sound (opt)
E792-8 : Space Invaders U1 (-35 only)
E792-10 : Space Invaders U1
E792-12 : Space Invaders U2 (-35 only)
E792-13 : Space Invaders U2
E796-11 : Rolling Stones U4 Sound
E796-15 : Rolling Stones U2 (-35 only)
E796-16 : Rolling Stones U1 (-35 only)
E796-17 : Rolling Stones U1
E796-18 : Rolling Stones U2
E796-19 : Rolling Stones U4 Sound (opt)
E811-22 : Xenon Voice ROM U1
E811-23 : Xenon Voice ROM U2
E811-24 : Xenon Voice ROM U3
E811-25 : Xenon Voice ROM U4
E811-26 : Xenon Voice ROM U5
E811-27 : Xenon Voice ROM U6
E811-28 : Xenon Voice ROM U7
E811-40 : Xenon U1
E811-41 : Xenon U2
E819-08 : Frontier U1
E819-07 : Frontier U2
E838-03 : Eight Ball Deluxe S&T sound ROM U4
E838-04 : Eight Ball Deluxe S&T sound ROM U3
E838-06 : Eight Ball Deluxe S&T sound ROM U5
E838-15 : EBD U2 ROM
E869-02 : Rapid Fire S&T sound ROM U5 (only ROM used on this board)
E869-03 : U6 for Rapid Fire
E872-06 : U2 for Mr & Mrs Pac-Man
E891-15 : U6 for Baby Pac-Man

The U2/U6 ROM software for EPROMs available here (bally 2716) and here (bally 2732) and here (stern). Below are the original ROM file names and numbers used in the 2732 ZIP file. This also gives an idea of which U6 ROMs are common between different games:

2732 U2 & U6 GAME ROM LIST
GAME U2 POSITION U6 POSITION
---- ----------- -----------
FREEDOM FREE2732.U2 FREE2732.U6
NIGHT RIDER NGHT2732.U2 720-2132.U6
EVEL KNIEVEL EVEL2732.U2 720-2132.U6
EIGHTBALL 8BAL2732.U2 720-2132.U6
POWER PLAY POWR2732.U2 720-2132.U6
MATA HARI MATA2732.U2 720-2132.U6
BLACK JACK BLKJ2732.U2 720-2132.U6
STRIKES/SPARES ST&S2732.U2 720-2132.U6
LOST WORLD LOST2732.U2 720-2832.U6
$6 MILLION MAN 6MI$2732.U2 720-3032.U6
PLAYBOY PLAY2732.U2 720-3032.U6
VOLTAN VOLT2732.U2 720-3032.U6
SUPERSONIC SURP2732.U2 720-3032.U6
STAR TREK STAR2732.U2 720-3032.U6
KISS KISS2732.U2 720-3032.U6
PARAGON PARA2732.U2 720-3032.U6
HARLEM GLOBE HARL2732.U2 720-3532.U6
DOLLY PARTON DOLL2732.U2 720-3532.U6
FUTURE SPA FSPA2732.U2 720-3532.U6
NITRO GROUND NITR2732.U2 720-3532.U6
SILVERBALLMANIA SILV2732.U2 720-3532.U6
SPACE INVADERS INVA2732.U2 720-3532.U6
ROLLING STONES ROLL2732.U2 720-3532.U6
MYSTIC MYST2732.U2 720-3532.U6
HOT DOGGIN HOTD2732.U2 720-3532.U6
VIKING VIKG2732.U2 720-3532.U6
SKATEBALL SKAT2732.U2 720-4032.U6
FRONTIER FRNT2732.U2 720-4032.U6
XENON XNON2732.U2 720-4032.U6
FLASH GORDON FLSH2732.U2 720-5232.U6
8 BALL DELUXE 8DEL2732.U2 720-5232.U6
FIREBALL II FB2-2732.U2 720-5232.U6
EMRYRON EMBY2732.U2 720-5232.U6
FATHOM FATH2732.U2 720-5332.U6
MEDUSA MDUS2732.U2 720-5332.U6
CENTAUR CENT2732.U2 720-5332.U6
ELEKTRA ELEK2732.U2 720-5332.U6
VECTOR VECT2732.U2 720-5332.U6
MR/MRS PACMAN MR&S2732.U2 720-5332.U6
SPECTRUM SPEC2732.U2 720-5332.U6
SPEAKEASY EASY2732.U2 720-5332.U6
BMX BMX-2732.U2 720-5332.U6
GRAND SLAM GRNDSLAM.U2 GRNDSLAM.U6
GOLD BALL GOLD2732.U2 720-5332.U6
X's & O's X&OS2732.U2 720-5332.U6
SPY HUNTER SPY-2732.U2 720-5332.U6
KINGS OF STEEL KNGS2732.U2 720-5332.U6
BLACK PYRAMID BLKP2732.U2 720-5332.U6
FIREBAL CLASSIC FB-CLASS.U2 720-5332.U6
CYBERNAUT CYBE2732.U2 720-5332.U6

You need to do some modification for new ROMs. The single 2732 mod at U2 is the best option for a -17 game in a -17 MPU.

Also that MPU needs some work done to be reliable. Those orange IC sockets are notorious for being crap. I service these boards if you dont want to do the work yourself. Message me for info.

Yes, you must "mod" each socket you are using an EPROM in. I've never "mixed" proms and eproms together and I'm unsure if you can do that or not... I would certainly advise against it.

As a rule of thumb, you should ALWAYS try to get the board repaired/booting AND jumper-ed correctly before you waste time modding it.

You can mix PROMs and EPROMs as long as you get the jumpers right. I always set these boards up for some kind of 2732 combo.

Ah, that's good info to know!

I know this is an old thread, but thought I would share some info I came across while bored...
I was looking at the “Bally ROM Part Number ID Chart”, which appears to be the same as what Clay had in his guide, and I noticed that neither had Lost World listed for U1 and U2. According to "Bally's chart for ROMs in a -17 MPU board”, FO-597 (this is the only reference I have been able to find to the ROM numbers), the numbers for U1 and U2 are as follows:
U1: E-729-39
U2: E-729-40

Also missing was Freedom.
U1: E-720-8
U2: E-720-10

And Six Million Dollar Man has an alternate listing of:
U1: E-742-5
U2: E-742-6

I don’t know if it’s anything of real importance, but I thought I would share.