820-4924 missing ppvout_s0_lcdbklt and ppvin_sosw_lcdbklt

imspotrepair

New member
Hello team Rossmann and Members,

Brief intro:
My name is Imran Osman
Live in Mombasa Kenya,
Have set up an independent repair and parts Apple shop been 2 years,
I am a self taught Apple repair technician but a Certified Mercedes diagnostic technician so I kinda have a clue on basic repairs.

Customer complaint:
No display on apple mac book pro 13 inch.

My findings:

Device charges well.
Device boots up with chime and fan runs.
No display on LCD.
No visible damage noted on J8300.
No water damage noticed under microscope inspection of board.


CARRIED OUT FOLLOWING TEST STEPS

TEST 1: J8300 pin 1 voltage check= 0.0V
RESULT: I beleive I should get 53v on pin 1 J8300

TEST 2: Checked PPVOUT_S0_LCDBKLT for short to GND at pin 1 J8300
RESULT: the line is NOT shorted to GND. Resistance keeps incrementally increasing.

TEST 3: Checked the following caps visually for signs of over heating or damage. C7760,C7761,C7762,C7763,C7764,C7765,C7766,C7767,C7 768,C7769,C7770,C7771,C7772,C7773,C7774,C7775,C777 6 AND C7717.
RESULT: None of the caps have signs of heat or water damage. All caps look happy.

TEST 4: Decided to check voltage on above caps.
RESULT: All caps read 0.0v on the positive terminals

TEST 5: Carried out dide test on D7710 and checked for voltage on each terminal
RESULT: Diode test was ok D7710 passes unidirectionally.
Voltage test = 0.0V

TEST 6: Checked coil L7710 for resistance
RESULT: 0.1 OHM OK

TEST 7: Checked caps C7710,C7711,AND C7712 for short to GND
RESULT: None of the above caps were shorted to GND.


TEST 8: Checked PPVIN_SOSW_LCDBKLT voltage on pins 6,5,2 and 1 at Q7700
RESULT: Voltage= 0.0 V
Comment It should be 12.9 v?

TEST 9: Checked voltage at pin 4 of Q7700 PPVIN_SOSW_LCDBKLT_R
RESULT: Voltage of 12.9 V present at pin 4 of Q7700



A major problem here in Kenya is availability of parts or for that matter even doner boards.
So I do not have a test LCD neither do I have a board to pick components from unfortunately.

My diagnosis led me to Q7700 AND U7700 simply because I reached a dead end since I could not
comprehend how the backlight circuit actually works and what factors activate the backlight circuit
on u7700 and thus q7700.

That said I placed a two weeks order for Q7700 and U7700, replaced both and here I am...........
still no voltages on PPVIN_SOSW_LCDBKLT and so no amplification and thus no voltage on
PPVOUT_S0_LCDBKLT. :(

QUESTION:
1.How does Q7700 work and switch ON?
2.Does Q7700 need to be switched ON by U7700?
3.If question 3 is a yes, then what factors trigger U7700 to switch ON Q7700

In short I need help.

Thanks and Many Regards from Mombasa Kenya
Imran Osman
IMspot Repairs.
 

2informaticos

Administrator
Staff member
First test should be checking for image with powerfull light on the back of Apple logo from the top cover.
If no image, no reason to look for backlight...

Also check if get 5V at J8300, pins 28-30 atleast few seconds, when you here the chime.
If missing, check voltages at U8300.
At the same time, pin9 should rise to 2.5V; if not, no image/backlight available.
 

imspotrepair

New member
Hello informaticos,

Thanks for the response.

1. using powerful light on apple logo, no image can be seen on LCD
2. At J8300 pin 28, 29 and 30 all have 5V present
3. pin 9 at J8300 rises to 3.31V

Kindly advise
Regards
Imran
 

dukefawks

Administrator
Very likely it is just an LCD problem. Get some cracked test assemblies and make sure that you use the correct year. 2015 machines do not work with 2014 LCD assemblies!
 
Top