(Another) PAPERBOY Sound Issue!!!!

Vanderzam

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I've been restoring a Paperboy cab for a couple of months now (I'm almost done). I've came upon a lot of problems and managed to fix them all. But since this cab seems to be cursed, a new glitch showed up last week: a sound issue.

As soon as I turn on the machine, you can hear this loud white noise, just like an old TV set on a bad channel. The sound comes only from the left speaker.

I ran the sound test in service mode, and it detected nothing wrong. I can also hear all the sounds playing normally on both speakers. It is as if this annoying noise was simply played on top of the music and sound effects.

I also replaced the AR-III with another one that I had in stock: same noise.

It cannot be the speaker itself because the "white noise" volume fluctuates when I turn on the service mode switch. It also fluctuates depending on the sounds played during the sound test.

You can check by yourself right here:

http://www.youtube.com/watch?v=Zya8F-EAFaY

Could it be the main board?
I've put so much money and time into this cab, any suggestions will be gladly welcomed!
 
Yes it could be bad DACs or bad sound generation chips on the main board. I think they are socketed but I could be wrong.

If they are socketed then it should be easy to rule out one out in turn. The audio is produced by two POKEY chips (marked Atari C012294) and a single YM2151. Power it off, pull one chip out and then power up, if the whine is still there then power down, replace the chip and pull out another. Hopefully the noise will vanish when you have the bad chip off the board. It may also be the DAC which takes the digital audio from the YM chip and converts it to analogue audio, that will be a YM3014, if that is socketed then pull that one on its own too. You will lose the audio from the YM2151 but the whine may also go with that.

Be very careful when putting the chips back that they go in the same way round, and that no legs get folded under when you push it back into the socket.
 
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Bingo!

You were right Womble, the troublemaker was one of the two POKEY chips. I replaced it and now the sound is perfect.

Thanks a lot for your helpful knowledge, I really appreciate!
 
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