For the iPhone series, below models with backlight integrate with screen.
- iPhone 6 series (6/6P)
- iPhone 6s series (6s/6sP)
- iPhone 7 series (7/7P)
- iPhone 8 series (8/8P)
- iPhone XR
- iPhone 11
(* the earlier models will not be introduced here)
In this article,let’s share the basic repair process of the backlight issues like no backlight, half bright half dim, etc.
First, replace another screen to exclude the possibility caused by the accessories.
Be careful when you do the screen replacement, do not damage the fingerprint button flex cable.
After that, if issue is still unresolved. Then check the cosmetic of the motherboard
- Check the whole motherboard under the microscope carefully to see if there is any obvious damage like components missing, corrosive, moldy, burning, etc.
- Focu on checking the display connector, check the cosmetic of connector pins to see if there’s any corrosive or deformation.
- Check the screw driver hold, to see if the motherboard get overly long screw damage sign
If find any abnormal, deal with the abnormal components first.
Can clean the PCB with PCB cleaner and brush slightly and carefully, but the ultrasonic machine cleaning is not recommended.
Thirdly, check the diode values on the display connector.
Especially the pins which related with the backlight function.
- For iPhone 6/6s/7/8, there are 3 backlight related signal rails
- For iPhone 6P/6sP/7P/8P/XR/, there are 3 backlight related signal rails
[ iPhone 6s display connector, there’re 3 rails related to the backlight function. ]
[ iPhone 6sP display connector, there’re 6 rails related to the backlight function. ]
Measure the diode values of the backlight function related pins.
- If the diode value is much more higher than the reference diode value, might be the resistor on the rail open or inner rail broken
- If the If the diode value is zero or much more lower than the reference diode value. It might be capacitor get shorted or chip damaged.
Track the abormal pin related rail, find out and replace the abnormal components with new ones.
Step 4, if the diode values are OK. Or after the step 3, the issue is still unresolved.
Then we should check the backlight related diode IC
Let’s take the iPhone 7 as an example to see the details.
Refer to the block diagram from Refox bitmap, to check the backlight boost/driver IC number and the locations on the motherboard.
After that, just track schematic/block diagram again. We can easliy find out the diode tube.
iPhone 7 display circuit related diode tubes are D3701 and D3702.
As the diode test pin is hard to touch
- I. We can find the pin connector components to measure
- II. Test with multimeter for two times. First time put the BLK/RED probes on the both sides, second time reverse the two probes. If measure result is one time around 200, another time infinate, indicate the diode tube is OK.
Step 5. If the diode compnents are OK and issue stay unresolved.
The we just go to the Backlight driver IC directly.
Remove the backlight driver IC, then measure the diode values on the pads.
- If find any pin diode value is abnormal, track the pad related rail. To find out and replace the abnormal components
- If all the diode values are OK. Then replace the backlight driver IC directly.
Tip
Based on the repair experience, if the backlight brightness can not be adjusted. Then we can also first go to the backlight boost IC. To replace it with a new one to have a try first.
OK, so this is the introduction for the iphone backlight issue repair process.
To know the more detailed working process, troubleshooting process, repair cases, etc. You can join the REWA academy to learn.