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sopranojam85

Q: Noisy audio from 3400c

Hello,

I just acquired a nice PowerBook 3400c. Everything works as expected, but the one thing nagging me is that the audio out circuit is rather noisy. There is whitenoise that is proportional to the system volume level, and there's quiet but noticable high-pitched interference that seems to correlate to the HDD seeking/writing.

This persists via both headphones and speakers. It persists when running just on battery, just on AC, and on both battery and AC connected, so does not change based on how the unit is getting power.

Anyone have experience troubleshooting/fixing this? This doens't sound like expected behavior, so I'm assuming that the age of this thing is the contributor. I haven't torn it apart for this specific issue, maybe there's a few capacitors I can change out?

PowerBook 3400c, Mac OS 9.1.x

Posted on Dec 15, 2009 2:38 PM

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Q: Noisy audio from 3400c

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  • by sopranojam85,

    sopranojam85 sopranojam85 Dec 15, 2009 7:05 PM in response to sopranojam85
    Level 1 (5 points)
    Dec 15, 2009 7:05 PM in response to sopranojam85
    As a side-note, I've checked all the audio input settings in the sound control panel. Neither the mic, line-in, or any other input listed is set to "play through output device," so it's not a settings issue. When I boot to the OS 9 install CD, issue persists, so pretty positive it's a hardware issue.
  • by sopranojam85,

    sopranojam85 sopranojam85 Dec 16, 2009 5:04 PM in response to sopranojam85
    Level 1 (5 points)
    Dec 16, 2009 5:04 PM in response to sopranojam85
    I disassembled the unit down to the logic board. There was only 1 large capacitor on the whole thing, and it was a tantalum cap, which my understanding is those last a lifetime. The majority of the caps which looked connected to the audio out jack were those microscopic on-board caps, that have unmarked capacitance -- I would have no way of knowing their values without having the schematic for the logic board, which only an Apple engineer from 1997 would likely have

    The sound out jack itself didn't have any cold solderings on it, or any dirt/debris, so I reassembled it. I suspect that I'm just going to have to find another 3400c out there to compare its audio out noise, see if this is an outlier or not.