iPhone 6s backlight issue after water damage - GSM-Forum

short_toground · 05-18-2017, 17:15

Have a 6s that had short on bl_anode capacitor. Replaced it.

No backlight so replaced u4020 still nothing.

Diodes are good, filters are good. Both coils have resistance that correspond to the schematic so presuming those are good.

There's no voltage boosting

Can someone test voltage at R4020 in a working 6s? It's a clock signal and I get 0v not sure if that should be 1.8v or not

Kradziej · 05-18-2017, 18:25

which cap shorted? C4023 i guess
with short in there its hard to believe that diodes survived. Change D4020 and L4020 anyway.

short_toground · 05-18-2017, 18:32

Quote:

Originally Posted by Kradziej

which cap shorted? C4023 i guess
with short in there its hard to believe that diodes survived. Change D4020 and L4020 anyway.

Yes the big cap C4023.

Do you know why the 6s uses two different diodes and coils?

Does the backlight switch from a low/high power function at some point?

Trying to figure out if backlight would work if only one of the coils/diodes were in circuit or if both need to be

short_toground · 05-19-2017, 03:06

Tried replacing coil and diode. Same issue.

Any ideas?

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Kradziej · 05-19-2017, 11:45

maybe there is more diodes in lcd so its using 2 coils to get more current, or maybe diodes are different in 6s, I dont know.
Still you dont need to change IC in water damage because its glued, problem is not in IC but somwhere around it

short_toground · 05-19-2017, 11:51

Do you have a working one to test voltage at R4020? Need to know if during operation it's 1.8v or not

Mine is 0v but schematic shows it's a clock signal so I imagine it shouldn't be 0v but can't verify

1.8v sdram trigger is present

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Kradziej · 05-19-2017, 13:05

I have 0v as well. Its clock line with pull-down so it should be 0 most of the times, you cant tell whats going on without osciloscpe.

short_toground · 05-19-2017, 13:12

Quote:

Originally Posted by Kradziej

I have 0v as well. Its clock line with pull-down so it should be 0 most of the times, you cant tell whats going on without osciloscpe.

Thanks for measuring that I appreciate it.

I couldn't measure for ac voltage at the switching side?

Do you know if backlight will work with only one diode/coil or needs both sets?

Thanks again

Kradziej · 05-19-2017, 13:44

Quote:

Originally Posted by short_toground

Do you know if backlight will work with only one diode/coil or needs both sets?

Thanks again

Ok we learned something hard way today. Dont turn on 6S with only one backlight diode because it damages backlight IC

short_toground · 05-19-2017, 13:45

Quote:

Originally Posted by Kradziej

Ok we learned something hard way today. Dont turn on 6S with only one backlight diode because it damages backlight IC

Oh boy lol sorry about that. Did it have backlight at all and then went out or instant no backlight?

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Kradziej · 05-19-2017, 13:59

Quote:

Originally Posted by short_toground

Oh boy lol sorry about that. Did it have backlight at all and then went out or instant no backlight?

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No backlight nothing just 400mA and then 18ohm on vcc_main. But if you think on it for a while then you have that coil which is charged by IC and then discharged through diode. If you have no diode then coil is pumped to very high voltages and damages transistors in SW1/SW2, thats probably what happened there. But thinking is not my strong point today, its too hot

.

emmanuelaboagye · 05-19-2017, 13:59

How to remove FRP on LG phones

short_toground · 05-19-2017, 14:01

Quote:

Originally Posted by Kradziej

No backlight nothing just 400mA and then 18ohm on vcc_main. But if you think on it for a while then you have that coil which is charged by IC and then discharged through diode. If you have no diode then coil is pumped to very high voltages and damages transistors in SW1/SW2, thats probably what happened there. But thinking is not my strong point today, its too hot

.

Lol yeah hot here too.

I wonder if both the smaller diode and coil were removed if backlight would work with just the bigger coil and diode.

But yeah at this point idk what to look for. Do you know if anything else enables the ic to switch besides 1.8vsdram?

Are the coils and diodes from a 6 compatible with 6s? I know they use different ic's

Kradziej · 05-19-2017, 14:15

Quote:

Originally Posted by short_toground

Lol yeah hot here too.

I wonder if both the smaller diode and coil were removed if backlight would work with just the bigger coil and diode.

But yeah at this point idk what to look for. Do you know if anything else enables the ic to switch besides 1.8vsdram?

Are the coils and diodes from a 6 compatible with 6s? I know they use different ic's

look at schematics, one diode is the same, and for coils just check parameters uH and A.

short_toground · 05-19-2017, 14:21

Quote:

Originally Posted by Kradziej

look at schematics, one diode is the same, and for coils just check parameters uH and A.

So if I change all diodes, coils, and ic and still no backlight. What could it be?

05-18-2017, 17:15	#1 (permalink)
short_toground No Life Poster Join Date: Jul 2016 Posts: 536 Member: 2598526 Status: Offline Thanks Meter: 52	iPhone 6s backlight issue after water damage Have a 6s that had short on bl_anode capacitor. Replaced it. No backlight so replaced u4020 still nothing. Diodes are good, filters are good. Both coils have resistance that correspond to the schematic so presuming those are good. There's no voltage boosting Can someone test voltage at R4020 in a working 6s? It's a clock signal and I get 0v not sure if that should be 1.8v or not

05-19-2017, 13:59	#12 (permalink)
emmanuelaboagye Junior Member Join Date: Sep 2016 Posts: 2 Member: 2627580 Status: Offline Thanks Meter: 0	Lg How to remove FRP on LG phones

05-18-2017, 18:25	#2 (permalink)
Kradziej Freak Poster Join Date: Sep 2015 Posts: 198 Member: 2453408 Status: Offline Thanks Meter: 63	which cap shorted? C4023 i guess with short in there its hard to believe that diodes survived. Change D4020 and L4020 anyway.

05-19-2017, 03:06	#4 (permalink)
short_toground No Life Poster Join Date: Jul 2016 Posts: 536 Member: 2598526 Status: Offline Thanks Meter: 52	Tried replacing coil and diode. Same issue. Any ideas? Sent from my iPhone using Tapatalk

05-19-2017, 11:45	#5 (permalink)
Kradziej Freak Poster Join Date: Sep 2015 Posts: 198 Member: 2453408 Status: Offline Thanks Meter: 63	maybe there is more diodes in lcd so its using 2 coils to get more current, or maybe diodes are different in 6s, I dont know. Still you dont need to change IC in water damage because its glued, problem is not in IC but somwhere around it

05-19-2017, 11:51	#6 (permalink)
short_toground No Life Poster Join Date: Jul 2016 Posts: 536 Member: 2598526 Status: Offline Thanks Meter: 52	Do you have a working one to test voltage at R4020? Need to know if during operation it's 1.8v or not Mine is 0v but schematic shows it's a clock signal so I imagine it shouldn't be 0v but can't verify 1.8v sdram trigger is present Sent from my iPhone using Tapatalk

05-19-2017, 13:05	#7 (permalink)
Kradziej Freak Poster Join Date: Sep 2015 Posts: 198 Member: 2453408 Status: Offline Thanks Meter: 63	I have 0v as well. Its clock line with pull-down so it should be 0 most of the times, you cant tell whats going on without osciloscpe.