[Trac #473] Keyboard keys occasionally stop working

[Zarro Boogs per Child]

#473: Keyboard keys occasionally stop working
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 Reporter:  mfoster  |       Owner:  mfoster
     Type:  defect   |      Status:  new    
 Priority:  high     |   Milestone:  BTest-2
Component:  distro   |    Keywords:         
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 Hi, Folks,

 On 11/16, when B1 units first entered final functional testing, we were
 there to watch what failures occurred.  Fairly quickly, a few units
 appeared which had keyboard failures where groups of keys would not work.
 Which keys would not work varied from machine to machine.  Though the
 keyboard appeared to be at fault, continued investigation revealed that
 the keyboard scanning microprocessor on the touchpad assembly was
 sometimes seeing latchup on its pins.  Latchup is a condition in a CMOS IC
 where a pin will be "stuck" at a high or low voltage.  When this occurs,
 the stuck pin prevents the keyboard microprocessor from seeing keys change
 state. Note that latchup only happens when excessive voltages are present,
 as when ESD (Electro-Static Discharge - i.e. a "static zap") occurs.

 The root cause of this problem is that the mechanical design in the B1
 systems does not properly ground the keyboard baseplate.  While an attempt
 was made to do this in the design, the metal components do not make proper
 contact with the grounded hinge assembly.  As a consequence, any static
 buildup on the keyboard can only discharge through the keyboard
 controller's scanning pins, then back up the PS/2 cable to the
 motherboard.  This leads to some keys on the keyboard not responding.

 While this was found and fixed on the same day, the true resolution was
 identified just as the last few B1 units were being built on the line, so
 all B1 units are susceptible to this failure.  The workaround is to power
 the system off and on again, which will reset the latchup condition in the
 keyboard microrocessor, and allow the keys to function once again.

 This will obviously be a very high priority fix for B2.

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Ticket URL: <http://dev.laptop.org/ticket/473>
One Laptop Per Child <http://laptop.org/>