No backlight when battery connected

Hi,
I have a MacBook Air 13" A1466 820-3209-A
There was corrossion under the backlight driver U9701 and no backlight. I changed the chip with a new one and now I get backlight but only if the battery is disconnected.
If I attached the battery I don't get backlight but I do get image.

Thanks in advance
 

2informaticos

Administrator
Staff member
Do PRAM reset first.

Post D7701 voltages, when no backlight present.
Also check SMC_LID signal, at same time.
Test what happens, if LIO flex is disconnected.
 
OK I'll assume it's D9701
When backlight not working :-
D9701 Pin 1 (PPBUS_SW_LCDBKLT_PWR_SW fluctuates between 7.27v and 7.52v
Pin 2 (PPVOUT_SW_LCDBKLT fluctuates between 7.40v to 7.52v
SMC_LID = 0v

** Now the backlight works on battery but as soon as I take the brightness up using the keyboard to maximum then the backlight dies again. If I close the lid and reopen the lid backlight comes back to life again.

Removing the LIO Flex makes no difference to the backlight
 

2informaticos

Administrator
Staff member
Yes, D9701; I was looking at 00165 schematic, by error.

SMC_LID must be high.
Check it disconnecting trackpad flex.
If still low, check R5071 value and traces.
 
My mistake I measuring at the wrong place. Yes SMC_LID is high and steady at 3.40v both when backlight works and when it doesnt. Is it possible the replacement backlight driver was bad or got damaged whilst I was heating it? Also it's ok to buy these chips off eBay right, I mean they are not programmed diffrently than ones off donor boards?
 

2informaticos

Administrator
Staff member
New chip is OK to buy.
I suppose you didn't get good solders.
Reflow it and try to solder U9701 properly.
 
You won't believe this but the chip I used for U9701 was wrong. Replaced with the correct chip and all is good now. Thanks again for your help - appreciated.
 
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