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Repair guides and disassembly information for Apple's 7th generation iPad. Released September 25, 2019. Model numbers: A2197, A2200, and A2198.

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No Display But Backlight Works. Microsoldering Question.

Hello.

I am working on an iPad 7 (2019) that came in for no display. Customer said the screen flashed green and then afterwards only the backlight was visible on the display. No image. The iPad is booting, as you can hear notification sounds and Siri.

I started by simply disassembling the iPad, disconnect the LCD flex cable, clean the connector, and reconnect. Same behavior. Backlight works, no image.

Next, I ordered a new LCD and installed. Same behavior. Thinking the LCD I was sent might be faulty, I received a replacement LCD. Same behavior.

I then removed the logic board and began diode mode tests on the LCD connector (J4100). All of my measurements are virtually the same as what is listed in ZXW Tools except for one pin and that's Pin 16 (EDP_HPD_EMI_CONN) that should be measuring around 1.690 according to ZXW, but mine reads 2.563 - quite a bit higher.

That pin connects to a resistor, a capacitor, another resistor, and an inductor. (R4190, C4190, R4191, and L4190). These 4 components all seemingly make up the EDP_HPD_EMI/EDP_HPD circuit. I measured the resistance of these components except for the capacitor which I just measured a diode mode reading on. I got the following measurements:

R4190: 7.48 kOhms

C4190: 0.483 (diode mode)

R4191: 20.04 kOhms

L4191: 1.2 Ohms

Unfortunately, I cannot know for sure what the proper values of these components are as I do not have another iPad 7 that works to check on. The two resistors in that circuit (R4190/R4191) reading quite different from another makes me suspicious. Then again, it may be totally normal. Without the schematic, it's hard for me to tell whether those two readings are supposed to be that way or if one of them (or both!) might be bad. I was hoping someone who might be a bit more familiar with this than me could look at what I have here and perhaps guide me on how to fix this problem or if I am even looking at the right place for the problem I am having in the first place.

I thought I'd mention that I did also check the EMI filters connected to J4100 and all of them seem to be fine.

I'm attaching a pic with my measurements on the components I have mentioned in this post. The added text in white is what I am measuring at each component. Thanks in advance.

EDIT: I just used the schematic from the iPad Air 2 and found the comparable circuit I am questioning (EDP_HPD_EMI_CONN). It looks like the 7.5 kOhm and 20 kOhm resistors are normal after all, so my earlier thoughts do not apply. So I guess I'm not sure what to do from here.

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Just for your reference here is a snip from the schematic for this specific circuit. The only thing that doesn't seem to match is the resistance for the inductor. The capacitor, I wouldn't be too concerned about regardless, unless it was shorted to ground or had a cold joint. Keep in mind that the other end of that inductor is technically also part of that circuit, and the EDP_HPD line goes to the CPU/SOC whatever you want to call it. Which theoretically could also factor into this issue.

Do you have an autoranging multimeter? Could the inductor actually be 1.2 kilo ohms or mega ohms? That would account for a higher diode reading and would definitely point to a blown inductor. And the sudden failure might also lead me to thinking a component failed suddenly.

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Hello. Thank you for your answer. Yes, my multimeter is auto-ranging. I tested the inductor a second time and it reads 1.2 ohms.

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I removed the inductor L4191 and replaced it with another inductor of the same specifications from the same circuit on the iPad Mini 2 logic board. Went back and diode mode tested pin 16 and I get the same measurement - 2.563 with a "new" inductor. The inductor itself reads 1.4 ohms when soldered on the board.

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@techwizards Hm. Welp. I would make sure everything is soldered to the board soundly, including the pin on the FPC. High diode mode reading is closer to the open end of the spectrum than short (to ground). I also have a known good one of these at home I can check for you when I get there. I know sometimes ZXW is off. But that seems pretty drastic. I will set myself a reminder, or I'm liable to forget.

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Thank you @flannelist . I will go back and touch everything up with some clean, fresh solder and if you would post your findings on your working iPad, that would be fantastic. Thank you again!

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@techwizards So. Just got home. I got a 1.91 on that pin in diode mode on my multimeter (it's a Fluke 115). And I got the same measurements as you on the components in question. So your reading still seems high.

So if the issue is with this line, it's still possible that the issue is related to the CPU. This model is pretty notorious for CPU related issues. And this is a pretty long trace. A diode mode reading that high is pretty uncommon on these boards. Does it look flexy or bent at all?

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Did you solve it? i'm having the same issue with an ipad 7 literally same problem, same readings everywhere and I can't solve it.

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