Small lightning flash across screen then nothing.
So I recently decided to go into Apple logic board repair after spending 3 years as an electronics apprentice for an automotive company and as a bit of practice I decided to have a go at fixing an ipad air 2 that my dad managed to destroy while removing the screen to retrieve a lost SIM card. Basially when you power the screen up there is a small lightning type flash across the screen then no display what so ever.
I've taken the device apart again, tested the inputs and outputs on the LCD socket and and found a couple of things but am not entirely sure if I'm just reading a few things wrong or if they even make a huge difference, so I'll try to be as concise as I can.
First: EDP_HPD_EMI_CONN has what looks to be a missing 7.5kOhm resistor on its output but as far as I know it is not a critical part of the system and should not cause no display(?)
Second: PP11v3_MESA_FILT seemed to have a short to ground. This being a critical BUS line (could be wrong, am in the very early stages of deciphering ipad schematics) I was pretty certain that this was the fault. So certain in fact, that I bought a spare board online for £30 to swap the few components I though to be responsible. However, upon testing the working board I found that it too had a missing PP11v3 line on pin 19 of the LCD connector.
So, the couple of things I would like to know are, first and foremost - am I reading these schematics "correctly" or as correctly as I can? Think Ive got the tracing pretty much down but all the abbreviations (What's PP? What's MESA? etc.) are throwing me and I'm finding it difficult to find answers on what they all mean so would like to know if there are any sources out there that could help?
Also, have any of you come across this lightning flash problem before? Is it even the logic boards or am I dealing with a dodgy screen? And finally, would the screen power up via the logic board using a bench supply with just the LCD, backlight and touchscreen connectors in place or would everything have to be plugged in? Sorry for the long list guys, just for the record I'm not lazy, I would rather figure this kind of thing out myself but am worried I'm sending myself in the complete wrong direction & would love some guidance by you fine people while I'm starting out if at all possible? P.S - all input/output filters seem to be doing what they should but have heard they can look like they work in circuit while actually not, could the filters be to blame?
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