#2452 LOW Untriag: backlight doesn't turn off (B4-14 SHF72050046B)

[Zarro Boogs per Child]

#2452: backlight doesn't turn off (B4-14 SHF72050046B)
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 Reporter:  Quozl     |       Owner:  mlj      
     Type:  defect    |      Status:  new      
 Priority:  low       |   Milestone:  Untriaged
Component:  hardware  |     Version:           
 Keywords:            |    Verified:  0        
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 The backlight does not turn off when directed.

 At the zero setting, there is light of a level lower than the minimum
 setting, but light is still emitted.  The light flickers a bit, at
 something between 5Hz and 20Hz.

 Every light level from 1 to 15 is different; each step yields a change in
 brightness in the correct direction.  The brightness is consistent with
 the other B4.  Both B4s are brighter than a B2.

 The backlight is off when the system is off.

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 '''Model''': B4-14 (received 2007-07-25 in a shipment of two, the other is
 fine.)

 '''Serial Number''': SHF7250046B

 '''Firmware''': Q2C18 (as received)

 '''Software''': 406.14 (as received)

 '''Diagnosis'''

 This is what has been tried so far:

  * bypass Sugar key and use ''/sys/class/backlight/dcon-bl/brightness''
 interface, no change to symptom, also verified that Sugar is indeed
 setting this value to zero,

  * bypass kernel and use Forth firmware '' select screen 0 a dcon! '', no
 change to symptom,

  * remove all power for a minute, no change to symptom.

 I'm prepare to open the system and diagnose further, if someone tells me
 where to look, since I need to place a recovery connector for EC work.
 I'm not NDA'd.

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Ticket URL: <https://dev.laptop.org/ticket/2452>
One Laptop Per Child <http://laptop.org/>