(Topic ID: 44545)

Volume problem after replacing U9 on Bally -32 sound board

By Marc

8 years ago

Topic Stats

  • 5 posts
  • 2 Pinsiders participating
  • Latest reply 2 years ago by stangbat
  • Topic is favorited by 2 Pinsiders


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    -32 sound 2 (resized).jpg
    -32 sound 1 (resized).jpg

    #1 8 years ago

    I haven't had to replace U9 (LM741) on a -32 in a while but had to today so I here's a quick write up for prosperity.

    This board (among other issues) had no sound output at all and U9 was the culprit. The problem when replacing U9 with something other than the original manufacturers LM741 is that you will still not be able to adjust the volume. There is a modification you can do that will allow this, basically you add a circuit that is found on the later -50 sound board. I'm sure there are other ways to go about it but this is how I do it.

    Start with the unmodified -32 that has had U9 replaced. Originally no sound at all and after replacing U9 sound is heard but volume control is still not available.


    Drill holes for mounting components.

    -32_holes_front.jpg -32_holes_back.jpg

    #2 8 years ago

    Make up components.

    U9_circuit_mod.jpg SDC10605.JPG SDC10606.JPG

    #3 8 years ago

    Modify board.

    -32_U9_unmodified.jpg -32_U9_modified.jpg

    #4 8 years ago

    Circuit installed and volume control now available.

    -32_modified_circuit_installed.jpg -32_modified_circuit_text.jpg

    5 years later
    #5 2 years ago

    This was helpful, I appreciate it.

    Here's how I did this modification. I replaced the LM741LN with a UA741CP and it works fine.

    -32 sound 1 (resized).jpg-32 sound 2 (resized).jpg

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