(Topic ID: 159032)

WPC A-12738 Needs to "Warm Up" for Good Audio?

By scupbucket

4 years ago

Topic Stats

  • 8 posts
  • 4 Pinsiders participating
  • Latest reply 7 months ago by Biglouie
  • Topic is favorited by 1 Pinsider


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#1 4 years ago

Is it normal for WPC A-12738 audio boards to get louder as the game warms up? I have the volume set at 7 which initially seems very quiet, sfx are faint, and barely any noticeable bass. After about 30-45 min of game play it gets louder and sounds great! For the heck of it I pulled the board and reflowed all connectors, reseated ROMs… no difference. Thoughts? Thx!

#4 4 years ago

Input reads a bit higher than 12v cold (normal?).

#5 4 years ago

Ok... I'm getting -12.1 and +11.9 at U3 and U4. Seems voltage checks out fine? From a lot of what I've been reading this in fact may be a capacitor on it's way out but I'm not sure which exact one to start at. I'm considering just replacing all the caps at this point. Soldering is fun.

1 week later
#6 4 years ago

Getting closer figuring this out I think. Here's what I did just in case anyone has a similar problem down the road.

I replaced the 47uf caps at C15, C18, C34, C36, C38, and replaced the 1uf tantalum caps at C46 and C47. While I was at it, I also corrected R23 and R24 to 150k ohm from the 56k ohm that were originally in place. Finally, I read about adding a 4.7 ohm / 2 watt resistor to the backbox speakers to bring the mids and highs down a bit allowing more bass to the foreground... holy crap what a HUGE difference!!! I can hear Arnold much better, I'm hearing sounds in the game I didn't before, very solid (not cabinet shaking) bass, and I can keep the volume up around 9-10. Sounds are clear even at higher volumes. Before I'd have it at 7 and it was just noise.

It still gets a tad louder after warming up but not a dramatic difference as before and the sound isn't all high end nails on a chalkboard. I still have some poking around to do...

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