#10974 NORM Not Tri: XO 1.75 - +3.3V_AUDIO is not driven

[Zarro Boogs per Child]

#10974: XO 1.75 - +3.3V_AUDIO is not driven
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 Reporter:  wmb at firmworks.com  |                 Owner:  wad        
     Type:  defect             |                Status:  new        
 Priority:  normal             |             Milestone:  Not Triaged
Component:  hardware           |               Version:  1.75-A3    
 Keywords:                     |           Next_action:  never set  
 Verified:  0                  |   Deployment_affected:             
Blockedby:                     |              Blocking:             
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 The voltage on U24 pin 5 should be 3.3V but instead it varies between 0
 and 2V depending on the mic bias voltage.

 Inspection of both the schematic and the gerber reveals that the
 +3.3VA_AUDIO net is connected to several loads, but is not connected to
 any voltage source.  Instead, it is getting its voltage from the mic bias
 supply via forward conduction of the top halves of D16 and D17.

 One result is that the AC/DC switches U24 and U25 do not work correctly,
 thus preventing the use of the loopback cable for audio testing.  Another
 result is mic signal distortion.

 The audio subsystem works much better with a blue wire from that net to
 +3.3V_AVDD at C218.  Perhaps +3.3V_AVDD and +3.3VA_AUDIO were supposed to
 be the same net?

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Ticket URL: <http://dev.laptop.org/ticket/10974>
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