Ipad 6th gen A1893 backlight issues

[mexkoala257]

Hello everyone!

First time posting here today so I am hoping i am doing this correctly. I have an Ipad 6th gen with back light issues. I can see a clear image on the lcd but it is not lit up. The ipad had never been opened prior to this happening and the digitizer was not broken either. I removed the digitiezer from the ipad and disconected the lcd from the ipad. I tested the 4 upper left hand side pins on the board for voltage and i am getting 4.2v on each one. I then tested the capacitors on each one of the lines and they are looking fine. I also tested the filters for continuity and they are looking good. They also do not show any signs of burn damage or physical damage. I continued to follow the lines to the diodes on each line and i am reading a .124 on each one way and a closed line on the other side. I am honestly at a loss as what is usually wrong seems to be testing right and i am not sure where to go from here. any help would be greatly appriciated!

Thank you!

[Jessa_the_Professa]

Did you do rule number one and test a known good lcd?
Are you sure the device isn’t under warranty? IPad 6th sounds really new. Never open an in warranty iPad outside of data recovery.

backlights only have sudden death in unopened devices IF they get short to ground. I can’t tell if you’ve completely ruled that out or not. You need one measurement—diode mode at the connector with red probe on ground. Line is either short or matches normal.

If the line is not short, you have no mechanism for sudden death of backlight in an unopened device. The category of backlight faults that are blown filters can ONLY happen through a problem at the connector and that happens at screen change.

so if the scenario is backlight anode line is not short and device was unopened, then most likely far and away is bad lcd.

Do rule number one.

[mexkoala257]

Thank you for your reply!

and yes i have tested two lcds one that was brand new from my supplier and one from another ipad 6 that i had here. I did the diode mode measurement and i am actually getting .288 on all 4 backlight pins with the red terminal on ground. I am thinking that shows a short to ground then if i am interpreting this correctly?

And the customer i repair ipads for cannot afford to use the warranty process for apple as they break and go through their ipads quite quickly on average i would say i am fixing 20-30 a week for them, usually broken screens and charging ports but from time to time i will see more complex stuff like this come through.

[mexkoala257]

One more detail that i came across that i am not sure if it makes a difference or not but if i test the voltage from the connector it shows a 4.17v which is also the current voltage of the battery. If i plug in the ipad i see it jump to 4.35v-4.5v. I am thinking that the voltage is not being amplified before it goes into the connector. Could it be the coil? I know thats not normal but im running out of ideas.

[Jessa_the_Professa]

The only practical backlight failure points for an UNOPENED iPad is that you have a bad LCD--most likely, bad connection--very rare, or a short to ground on BOTH the backlight anode lines--that would be incredibly unlikely. Backlight is a simple circuit and it really only has the failure point of short to ground. You need only one measurement--the diode mode reading on iPad 6 backlight anode line AND you need to know what known good is. Compare to another iPad 6. See whether or not there is a difference. We have no way to know if 0.288 is normal or low--it would be low for an iPhone 6 but normal for an iPad Air. You have to figure out what the normal value is for iPad 6.

There is no point in taking voltage measurements for backlight--if backlight is working you'll have full backlight voltage. If backlight is not working, you'll have battery voltage because some part of the system is wrong--chip, coil, diode, filter, connector and the system is not boosting voltage. It tells you nothing that you don't already know "something's wrong"