820-3437 no backlight

2informaticos

Administrator
Staff member
Do you get image for sure?

Check XW7720 for continuity; lot of info available on the forum.
Inspect U7701 for corrosion; pay atention to B1/2 balls.
 

bartech

Member
i change u 7701 still the same, on c8317 power is droping slowly from 19-8,5v any idea?
there is apple logo but no backlight
 
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2informaticos

Administrator
Staff member
So backlight boosts and drops immediately.
Usually bad feedback trace, in this case.
Did you really check continuity from D7701 and ball A5 of U7701?

Be sure all R7717-22 are good.
Check diode mode to ground on each one; should get very similar values.
Also test with known good LCD.
 

bartech

Member
u7701 check lines :

1-gnd
2-gnd
3-1
4-1081
5-1
6,7- 1600 rising to 2000 then 1
8-1324 slowly rising
9-1434 slowly rising
10-gnd
11-1410
12-1420
13-1
14-532
15-1
16-1416
17-1944 for sec then 1
18-844
19-844
20-1
21-1
22-1
23-1
24-gnd
25-1
 
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2informaticos

Administrator
Staff member
Seems that you didn't read "How To collection" thread.
Now take the red probe of your multimeter and keep it on the ground.
Check all test points ONLY with black probe!

BTW, use signal name, or component point; better to use U7701 ball marked on schematic.
You are working one board at time; one pdf, one boardview.
I have approx 20 pdf schematics opened (for online support) and ONE boardview of the board I work on the desk.
Don't force me to open more; no need that, once pdf has all I need to reply.
 

bartech

Member
3-on r7715 - 568
4-on c7704 - 553
5-on d7701 - 595
6,7 on d7701 - 428
8 - on r7714 - 554
9 - on r7716 - 568
10 - gnd
11/ 16 - on c7710 - 424
12 - on u7701 - 565
13 - on tp7701 - 554
14 - on c7711 - 347
15 on r7719 - 633
17 on r7755 - 565
18 - on r7753 - 494
19 - on r7757 - 495
20 - on r7718 - 636
21 - on r7722 - 630
22 - on r7721 - 629
23 - on r 7720 - 628
24 - gnd
25 - on r7717 - 631
 
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