(Topic ID: 203963)

Bally Sound boards: 2518-32 vs 2518-50

By CadillacMusic

1 year ago

Topic Stats

  • 7 posts
  • 4 Pinsiders participating
  • Latest reply 1 year ago by CadillacMusic
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#1 1 year ago

Got a Harlem Globetrotters I'm bringing back from the dead. For whatever reason, I can't seem to find the sound module that was originally in it. I've got a spare 2518-32, but no spare -50. Is it possible to convert the earlier to the later? What's the difference? Also, what's the kind of chip needed for u3?

Edit: Changed 51 to 50. Do not post before coffee.

#2 1 year ago

No, they're different sound boards.

You're in luck, though. The sound boards have been re-made here: http://nvram.weebly.com/new-pcbs.html

#3 1 year ago

I'm sorry, it's the -50, not 51.
Lemme edit that.

#4 1 year ago

What is the difference? Different resistors? There's gotta be a way to convert it, as they're so similar.

#5 1 year ago

You should only convert it if the idea seems fun or challenging. If not just buy the excellent replacement board.

First determine if the -32 you have works. You can install it in the HG and try it. The tunes will be wrong but if it's working it will at least make some sounds of different frequencies. This of course is not a comprehensive test.

You'll need to change the jumpers per this page:


Then you'll need to replace U3 with a 729-51 PROM. These are unobtainable except from a scrap board but there is a conversion kit that uses a 2716 EPROM:

http://nvram.weebly.com/repair--conversion-kits.html. If you have an EPROM burner you can make the 2716 EPROM yourself from the file provided.

There may be other small circuit differences too; compare the schematics, which you can get from ipdb.org.

#6 1 year ago
Quoted from CadillacMusic:

What is the difference? Different resistors? There's gotta be a way to convert it, as they're so similar.

the -50 board has the C and D jumpers. The -32 board is missing those jumpers and is hard wired essentially with the D jumper.

To make a -32 sound board play as -50 board with the 729-51 prom. Slice and jumper so C would be installed as the -50 board schematic. Cut out C22 and R28. Change to the 729-51 PROM.

The -50 board also has better support for the 741 chip with the addition of voltage divide and smoothing cap at R37, R38 and C23. You likely need to do this mod if you replace the 741 amp. New manufactured amps do not play nicely with the hackish way bally used it on the -32 board.

#7 1 year ago

Awesome. Thanks! Just what I needed. Probably not going to be able to get the boss to spend $125 on a new board, but $25 on a conversion should pass the cost test.

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