[Trac #977] Suspend/resume causes a popping sound

[Zarro Boogs per Child]

#977: Suspend/resume causes a popping sound
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 Reporter:  wmb at firmworks.com  |        Owner:  wad     
     Type:  defect             |       Status:  assigned
 Priority:  blocker            |    Milestone:  BTest-3 
Component:  hardware           |   Resolution:          
 Keywords:                     |  
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Comment (by wmb at firmworks.com):

 The following hardware modification eliminates the pops (with reference to
 the B2 schematic):

 a) Change R337 from a pull-up to a pull-down (to AGND).
 b) Remove R335
 c) Remove Q43
 d) Put a 10K resistor across Q43 pads 2 and 3

 This change results in the net elimination of one component, a transistor.

 It requires that the audio driver must explicitly assert the EAPD signal
 in order to power on the amplifier.  This is a change in the sense of that
 signal; asserting it used to power off the amplifier.  I know of no way to
 avoid this inversion (other than moving the amplifier shutdown control to
 a completely different GPIO pin).

 Existing boards can be reworked fairly easily:

 1) Move R337 to the otherwise-unused pad for the (unstuffed) C508.
 2) Remove Q43
 3) Move R335 to pads 2,3 of Q43.

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Ticket URL: <http://dev.laptop.org/ticket/977#comment:5>
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