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iPhone 8+ no backlight
Got in an other strange one... iPhone 8+ liquid damaged, but no corrosion that I can see anywhere on the board. It had water in the phone, but we were able to dry it out with mild heat for about 5 minutes. New screens all produced no backlight, but there is image. Diode mode readings are close to ZXW's data except one pin (#19) which went to chestnut. The 240 ohm resistor reads 240 ohm on my meter. I replaced chestnut to rule it out and still no backlight. Diode mode readings around both backlight drivers seem correct against a known good board. Any ideas?
That was the only pin that was off according to ZXW and I didn't think it had anything to do with the backlight since chestnut is display and touch, but...never know 😛 The readings from the board are :
Pin | Reading | ZXW | Difference
47 | .609 | .585 | .024
45 | .515 | .469 | .046
43 | .609 | .585 | .024
41 | .608 | .585 | .023
39 | .512 | .469 | .043
37 | .609 | .585 | .024
You can definitely see an image on the screen right? If so and you are getting the correct diode mode readings at the connector, then you're probably looking at two bad coils (unlikely) or a bad data line that goes to both backlight ICs. I believe that there are only 2-3 data lines that go to both backlight ICs, so that should narrow down your focus. It's also possible that the pins on the connector are bent. I think the next thing that I would do is to measure the voltages going to the anode lines with the phone on and the screen powered on. They should both be greater than 10V. You just want to make sure that it's not a connector issue. You can also remove one backlight ICs and measure the data lines (DWI) to make sure that they are not OL.