[Trac #685] Failure to power up

[Zarro Boogs per Child]

#685: Failure to power up
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 Reporter:  Quozl     |       Owner:  mfoster  
     Type:  defect    |      Status:  new      
 Priority:  low       |   Milestone:  Untriaged
Component:  hardware  |    Keywords:           
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 Sometimes a unit will fail to power up when asked to using the power
 button.

 The symptom is that a click from the speakers is heard, the power LED
 lights up, the wireless LED lights up, but the expected light-up of the
 display does not occur.

 Holding the power button down to turn off, works fine.  Turning the unit
 back on reproduces the problem.

 Workaround is to remove external power, remove battery, wait ten seconds,
 then restore.

 Problem has been observed on all three units.  One unit did it yesterday,
 two units did it this morning.

 The history of the units ...
  * several days ago EC Q2B16 was installed,
  * several discharge and charge cycles have happened,
  * about 14 hours previously, a one-hour discharge to about 60% capacity,
  * charged to full capacity,
  * left overnight powered down with batteries but without AC supply, room
 temperature 29C to 24C.

 The discharge and charge cycle was monitored ... I have logs of voltage,
 current, capacity and temperature during it.

 May relate to ticket #637, except that the batteries are not low, and are
 able to run the units fine after a removal.

 Actions following:
  * removed AC power,
  * took batteries out of units to measure voltage open circuit, each
 battery pack shows 6.75V, 6.75V and 6.73V,
  * inserted batteries, but not AC power,
  * powered up (each unit powered up fine),
  * began monitoring, first sample of psu_0/voltage shows 6512, 6450, 6448,
 voltage declining as expected, but not particularly low.

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Ticket URL: <http://dev.laptop.org/ticket/685>
One Laptop Per Child <http://laptop.org/>