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La suggestion est de remplacer R18 d'une 220 Ohms en 100 Ohms. David qu'en penses-tu ?Reducing Hum on Type1 System3/4 Sound Boards.
As documented by G.Sylvain. Early type 1 sound board games can have noticeable hum in the speaker, especially bothersome during game-over mode. The hum would not be affected by the position of the volume control on neither the cabinet nor on the sound board itself.
I made sure all screws on all boards were present and tight, along with clean brackets, to ensure a good ground connection. That did not help. The second and most obvious problem are old electrolytic capacitors on the sound board, mainly C10, C30 and C29. These were replaced with new ones to no avail. I even replaced the amp's feedback capacitor C13, and again no help.
I noticed that the hum would be greatly lowered if I reduced the type1 sound board resistor R18 from 220 ohms to 100 ohms. This resistor controls negative feedback to the TDA 2002 audio amplifier, thus the overall gain/volume. On more modern Williams sound boards with speech such as Black Knight, the hum is almost zero, while the final audio amplifier circuitry is essentially the same (except for one additional 1K resistor and a different cap value).
Changing R18 to 100 ohms will reduce the maximum audio volume of the game, and the volume must be turned up. I felt that the maximum sound level was still powerful enough for most home-use applications. Besides, it lowered the hum enough to make this 'work-around' fix quite acceptable.
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