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Old 04-15-2022, 11:06 AM   #1
grimacelord
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Join Date: Jan 2017
City & State: Atlanta, GA
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Posts: 140
Default Apple iPad Pro 3rd Generation 12.9" (A1876) No Power/Charge When Screen Is Connected

Hello.

Working on an Apple iPad Pro 3rd Generation 12.9" that has a weird issue. When the display is NOT connected, the iPad will charge and power on normally. I know it's on because I can hear notification sounds and the charging notification sound.

If I connect a brand new display to the logic board, the iPad will not turn on at all. When I connect the iPad to an 18W wall charger and a USB-C ammeter, I can see that the iPad is attempting to charge, but constantly "resets" after just a moment or two.

For example, when I connect the iPad to the ammeter and 18W charger, the ammeter's display will initially read 5V and about 0.90A. The amps will move up to about 1.2A and then the entire ammeter's display goes blank (as if I unplugged it from the wall) and then the entire process starts over in an endless loop.

When the screen is not connected, the charging behavior appears completely normal for this model which is 8.93V and 1.87A holding steady.

I have experimented with the 4 display connectors to see which connector seems to be the culprit by removing one of the 4 cables at a time and retesting after each one. I found that the LCD connector (labeled Connector 1 in my image below) is the one that seems to be at fault. When I have the ribbon cable attached to that connector, the iPad will not power or charge. When I disconnect that cable, but still leave all 3 of the others, the iPad will power and charge normally (but of course I cannot see anything on the screen because that connector is for the LCD)

I have tried two different displays and they both behave the same way.

I then thought I would see if there are any diode mode readings of the pins for the LCD connector. I found some online, but my readings seem to be quite a bit different than what is shown on the image I found. I have taken measurements and edited a photo to show what my measurements read versus what I found on the logi.wiki website here. My measurements are the ones in red whereas the original photo's measurements are in white. If I haven't put a red measurement next to the white one, it is because I am reading the same. The only red ones is if I am reading a different measurement than what the original photo listed.

Thanks

EDIT: And just as a side note, my measurements more closely resemble the listed measurements on logi.wiki for the iPad Pro 4th gen. ZXW does have part/circuit names listed for the 4th gen, but not the 3rd. It seems like I could likely use the 4th gen boardview to help me with my 3rd gen.
Attached Images
File Type: png MYMEASUREMENTS.png (534.7 KB, 12 views)
File Type: jpg 1200px-iPad_Pro_1293_Overall.jpg (221.3 KB, 9 views)

Last edited by grimacelord; 04-15-2022 at 11:25 AM.. Reason: more info
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