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820-3476 intermittent LCD issues

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  • dukefawks
    replied
    IS there an image without backlight now?

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  • Rford
    replied
    dukefawks, U8300 change again, intermittent display/backlights. It seems like after a while u8300 is getting blown, but presently, I get a flicker on the LCD, but the weird part is I'm getting display and bcklt voltage even though it is showing nothing (no glow and no display). When I turn it on, it gives a brief glow and flicker of life though.

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  • Rford
    commented on 's reply
    Definitely known good LCD. do you know what known good LED BKLT voltage drop should be on diode mode? If it's high what does that mean? Too high resistance somewhere correct?

  • dukefawks
    replied
    Need to rule out the LCD. Try a known good assembly.

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  • Rford
    replied
    dukefawks any other ideas? CPU?

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  • Rford
    commented on 's reply
    dukefawks larossmann smc_lid is 3.40 out of machine, no 5v pulse, no en signal at r8319. Went up the circuitry, all resistors within spec. Could it be the cpu?

  • dukefawks
    replied
    Why did you replace it? Did you make sure there was an enable signal on R8319? I bet it's not there. Check L8300 again when you turn it on and see if you get a short "pulse" of 5V there, will be very short so hard to catch on multimeter, better with scope.
    Also check SMC_LID first of course, must be high.

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  • Rford
    replied
    yes, yes, 0V at L8300... Tried working up the circuit. Led me to U8300, where its getting VCC but no outputs. Replaced... Nothing yet. Checked for short, .401 voltage drop.

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  • dukefawks
    replied
    Does it still chime?
    Have you tried a known good LCD assembly?
    Is there 5V on L8300?

    Leave a comment:


  • G.Beard
    replied
    I would look at page 58 on the schematic and start testing for values. Check what's going to and from the LP8548, etc.
    Last edited by G.Beard; 08-24-2016, 11:23 PM.

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  • Rford
    commented on 's reply
    My bad. Minor liquid damage, seemed to be concentrated around the battery connector, and the keyboard backlight connector. The components near the kb bl connector were fried, so I replaced them and it seemed to work. I put the board aside to begin on another, came back and it didn't work anymore. No BKLT voltage and no display voltage.

  • larossmann
    replied
    Need history to provide answers! Drop, liquid, keyboard replacement, etc.. what happened to this?

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  • Rford
    started a topic 820-3476 intermittent LCD issues

    820-3476 intermittent LCD issues

    I have another 3476 Retina, had display and backlight... suddenly stopped. No voltage at connector (Bcklt or display). Does anyone have any tips? I also would like if anyone has known good, voltage drop values for pins.
    TIA

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