buzz fix

Joerg Reisenweber joerg at
Wed Mar 4 09:09:50 CET 2009

Am Di  27. Januar 2009 schrieb Paul Fertser:
> Al Johnson <openmoko at> writes:
> > On Monday 26 January 2009, Christoph Siegenthaler wrote:
> >> are there any updates from resellers, FIC or any half-official
> >> DIY-tutorials on the hardware problems, i.e. the buzzing?
> >
> > This appears to have benefited from feedback regarding capacitor types 
> > the few people so far to have attempted the mod, 
> The feedback is that: you can use any cap, including tantalum. :)
> > but more feedback is requested. The lack of feedback from people
> > trying it may be why it hasn't yet made it past release candidate
> > stage.
> No more feedback is really needed. Everyone who performed the rework
> confirmed that it eliminates the buzz. No single negative report. And
> i guess at least 10-20 people have already tried the rework. So, the
> reason that no reseller is doing it yet is probably due to
> communication/business issues rather than technical.

I'm not in charge any more to push this fix, but to me it seems we really 
don't need to quantify "how much it improves" buzz-issue.
The cause and ways to creep in of buzz are well understood by now by some guys 
at least (and NO it's NOT the mic catching RF near antenna, it's pin4 of 
hs-jack), the bigC-rework is evidently (based on empiric and EE basics) 
eliminating the ripple we see on MICBIAS, and a gsmhandset.state file 
correctly using differential input mode (control.63 value "Mic 2") won't 
break audio function from unfixed to buzzfixed FR.
Also we don't need any sophisticated test procedure, as
* all devices are prone to buzz issue, so we don't need to prove there is buzz 
before fix
* the big-C rework will either kill the buzz or you find you did sth wrong and 
mic stops to work. So any engineer doing the actual fix doesn't need any 
sophisticated "fix succeeded" test more complicated than that involved in 
replacing a lightbulb. Test call -> works -> fine.

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