820-3476-a chime with grey onscure beeld

[LaptopRepair]

Hello;

my next macbook gives chime when pressing power button. then after 4 or 5 seconds a flits light comes on the screen then become black. i still see a little bit light on screen. And that is it.

what are the first steps to be done on this situation?

 

[dukefawks]

Liquid spill? SMC_LID high? Check backlight chip area for corrosion.

 

[LaptopRepair]

After a look to the board I saw no liquid corosion traces.
What do you mean with SMC_LED high?
which IC is the backlight chip?

 

[MDY]

Duke said LID, not led.
Backlight chip is LP8545
Check schematic and see which chip creates Vled out for screen.

 

[MDY]

U7700
lp8548

 

[dukefawks]

Voltage on SMC_LID? Inspect for corrosion around U7700.

 

[LaptopRepair]

SMC_LID is 3V44. and I don't see any corrosion arround the U7700

 

[dukefawks]

Got another LCD assembly to test?

 

[LaptopRepair]

I ve just tested the pin1 of the LVDS connector. it got no PPVOUT_S0_LCDBKLT.
then D7710: Anode has 12V7 but cathode zero. feedback is missing. what can it be?
maybe short R7732? will test in a minute.
No voltage devider is ok.
Q7701 gate is low 1V7. need to be more then 7V. pin1/2/3 are zero, and pin5 is 12V. will this mean the the U7700 is dead?

 

[dukefawks]

This can only happen when D7710 is dead/open. I have never seen this happen, test D7710 on diode mode.

 

[LaptopRepair]

Already done. seems to be normal. in diode mode test gives 0V3 forward. and in sper it gives zero.

 

[dukefawks]

Then there must be voltage on both sides.....

 

[dukefawks]

Are you measuring this with LCD plugged in? Q7701 is switching so nothing interesting to measure there.

You must verify this board with another LCD assembly to be sure it is ok.

 

[LaptopRepair]

Yes indeed. i was measuring with lcd plugged in. if measuring without LCd voltage must be there?
will test after 2 hours from now

 

[dukefawks]

Without LCD voltages will NOT be there.

 

[LaptopRepair]

Right. just tested and voltage was not there. Is another working display manatory or is there another methode?

 

[dukefawks]

Get a test assembly, a cracked one or something. Where are you located?

 

[LaptopRepair]

I m in The Netherlands.
And indeed I ve borrowed an LCD from a working mac. And indeed image showed up. thanks.
But there should be a way; a signal coming at the LVDS connector or from the LCD to the SMC for example that can confirm this problem, I presume.

Now the we know that the problem is the LCD. can we fix this issue if we disassemnle the LCD?

 

[dukefawks]

Buy a complete assembly! Make sure to order for the correct model year.

 

[LaptopRepair]

Okai. But how can you confirm that the LCD is dead by measuring signals on the LCD connector?