Mic volume extremely soft after buzz fix with SHR unstable

Al Johnson openmoko at mazikeen.demon.co.uk
Mon Feb 22 22:36:20 CET 2010

On Monday 22 February 2010, Jan Girlich wrote:
> Am Montag, den 22.02.2010, 17:25 +0000 schrieb Al Johnson:
> > It can be hard to tell whether the joint is electrically good just by
> > looking at it, and solder connections on those components are tiny. You
> > really need to use a meter to test it, and I expect this was done by
> > whoever did the fix for you, so it probably isn't the problem. If you are
> > competent to test this, or know someone who is, the schematics and fix
> > SOP are both available:
> >
> > http://people.openmoko.org/joerg/GSM_EMI_noise/big-C_rework_SOP_rc2.pdf
> Okay, the joint I suspected to be broken seems fine. It's the one on the
> left of the two red arrows in the above description. That's where my
> capacitor is connected to and I just checked the the resistance from the
> capacitor to the pad where the right red arrow points at. No measurable
> resistance, so the joint should be electrically good.
> > > > Controls 48 and 12 are on maximum, while control 5 has 12 steps
> > > > remaining. You still have scope to make the mic a fair bit louder if
> > > > you need to. 3, 5 and 121 would give the same volume level with less
> > > > chance of distortion.
> > >
> > > Tried it. Still so soft that you have to yell really loud at the phone
> > > and only hardly can hear anything on the other end. I'm usually testing
> > > with my stereo, turning it on and putting the phone on the speaker. But
> > > I have to turn my stereo to levels it's getting uncomfortably loud just
> > > to hear a faint noise over the phone.
> >
> > So 3, 7, 127 is still too quiet? In that case something may be wrong.
> > Check the buzz fix, and also that the hole in the case isn't blocked.
> Checked it, the hole is free.

And the rest of the buzz fix? Check the resistance of R4303 (mic case to gold 
ring) as described in the SOP. It should be 2k2. Also look for shorts between 

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