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[SOLVED]A1502_820-4924-A No backlight after water damage

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crea2k

New member
No backlight on A1502_820-4924-A after water damage.

Pin 28 on lcd connector - PP5VR3V3_SW_LCD was corroded, re soldered this.

Pin 1 on lcd connector - PPVOUT_S0_LCDBKLT in diode mode shows OL in both directions in diode mode, in resistance mode shows high, then low, then high then low, like a discharging capacitor.

D7710 = 306/OL
Q7701 visual = looks ok
Q7733 = OK
U7700 = OK
R7700 = OK
Q7700 visual = looks ok
R7702 = OK
R7701 = OK

Suspect U7700 / LP8548B1SQ_-04 so have ordered one of those in.
 
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dukefawks

Administrator
Do you have an image? Hold flashlight to Apple logo in the back. U7700 almost never dies, that is the last thing to replace.
 
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crea2k

New member
What usually dies ?, iv ordered in Q7700 and also Q7701 as I cant see much else that iv not tested that would be critical for this.
 
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JohnB8812

New member
Have you replaced or removed the LCD connector yet? If it was corroded to begin with, best to replace it could be internally corroded or shorted. Remove it, and see what you get in diode mode on BKLT output (do not apply power of course).
 
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crea2k

New member
No the only corrosion on the connector was on pin 28 which I have re soldered, none of the other pins have any corrosion at all on them. How does a connector get internally shorted as the pins just go from the pad to the connector through a bit of plastic ?
 
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crea2k

New member
Just tested and im getting 52.2v @ the connector on pin 1 (pad side) when the screen is connected and powered on.......so confused now.
 
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JohnB8812

New member
They get shorted internally by corrosion and burning. 52 volts suggests the boost circuit is working, but it doesn't see the load (light of the screen). Have you tried a known good 2015 screen yet? Has to be 2015 2013/2014 will give you no backlight.
 
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crea2k

New member
No I dont have any screens, if its the screen the customer will scrap it I think. Is there no way of testing it without another screen ? . The only screen I have is the original one.
 
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crea2k

New member
It looks fine, iv just thought I have a bunch of broken screens under the desk with cracked lcd, so il see if any of those are compatible.
 
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crea2k

New member
Is there a way to tell what year they are other than comparing the lcd / webcam connectors ?, as they all just in a unmarked pile.
 
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crea2k

New member
SUCCESS !!
So I took the screen apart, and was about to dismantle the lcd from the backlight when I noticed the cable that plugged into the lcd end didnt look in the best of shape and was corroded. So I took the cable from the other screen I had and replaced that and it now works. Which is brilliant as I really wasnt looking forward to transplanting the lcd unit across. So if in doubt strip the screen down first and inspect both ends of the cable !.
 
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