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Portable 5120 Screen Contrast slider


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I just got it running today! However since the first time booting it I have not been able to adjust the contrast since. It seemed to change on its own after a boot cycle to a slightly lower contrast and since then moving the slider up or down does nothing. already tried disconnecting the battery and letting it sit a few along with reseting the power manager, I also checked to see if it had a preference but there was none to delete.  Any ideas?

 

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Edited by History_SE30_Dude
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Glad you got this running at least.  Have you verified the 5V always on rail is actually 5 volts?  And the 12 volt rail too?

 

Display contrast is generated by the power manager chip, from pin 57 (see page 12 of portable schematic).

I'm no expert on the display contrast side of things, but here's a list of possible issues:

  • A communication break between the system and power manager (software or hardware)
    • Check pin connections between the power manager and VIA chip, that's how the power manager talks to the rest of the system
    • This isn't hugely likely because if there was a communication issue then the system would probably refuse to boot with a power manager test error
  • Traces or components degraded in the contrast generation area
    • Connections between power manager, Q18, Q19, and associated resistors/capacitors should be checked with a meter
    • You may want to remove the transistors from the board and specifically test them
  • Traces or components degraded in the screen itself
    • Probably the most unlikely option in the list, because as I recall the display uses tantalum capacitors (nothing to leak)
  • The power manager chip could be damaged and changing the setting won't do anything even if it's communicated properly
    • Maybe the PWM driver is stuck at a particular frequency due to invisible damage from capacitor fluid or over-voltage from use with bad capacitors

 

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