#10953 NORM Not Tri: XO-1.75 External Mic sense does not work

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#10953: XO-1.75 External Mic sense does not work
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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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 It is not possible to detect the presence of an external MIC from
 software.  GPIO 96 reads back 0 in both cases - when something is plugged
 into the ext MIC jack and not.

 The voltmeter reading on the EXT_MIC_PLUG net is 0 when nothing is plugged
 in, and 1V when a plug is inserted.  1V is probably below the threshold of
 the 3V3 GPIO pin.

 The voltage on the high side of the R363 pullup is the expected 3V3.

 I suspect the problem might be parasitic conduction through Q9, as the
 voltage on Q9 pins 1 and 2 is 1V with a plug inserted.  Q9 pin 3 is at 1V8
 in that case.

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Ticket URL: <http://dev.laptop.org/ticket/10953>
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