iPhone 3GS no backlight coil is OK

[wildwild]

Hi all,

I have a dropped 3GS phone with no backlight when tested with good working LCD screens. The 6R8 coil measured 0.8 Ohm so it must still be OK.

Pin 1 of 109 IC to pin 3 on LCD connector is still OK (0 Ohm).

No water damage to the iPhone.

What else should I check?

Thanks.

[wildwild]

Also, how else do you confirm that the 6R8 coil is still OK?

Correction: It was pin 6 of the 109 IC to pin 3 on LCD connector is still OK (0 Ohm)


Thanks.

[Reinsaddict]

Just follow the masters guide: http://forum.gsmhosting.com/vbb/f631...cture-1409330/

post number 9. Continuity on the coil says nothing about whether is works well.
Follow post nr 9.

[wildwild]

Thanks,

This one got me stumped. There is 4V on pin 3 of the LCD connector. This means that the 6R8 coil and the 109B IC are working as they should but still no backlight

Help anyone?

[MeiTeS]

check this solution..check if you not have missing components .. thx Wites for picture..

[Wites OM Tesla]

Originally Posted by wildwild

Thanks,

This one got me stumped. There is 4V on pin 3 of the LCD connector. This means that the 6R8 coil and the 109B IC are working as they should but still no backlight

Help anyone?

This is good but 4V can be even if coil is bad so when lcd is connected it must generate around 12V to 16V understand.

[wildwild]

Thanks Wites,

I had a look at the 3GS schematic diagram and still could not work out why it would not work. If the coil is bad/open circuit then there should not be any voltage at pin 3 of LCD connector at all. The 4V was when the LCD was not connected.

One other possible fault is the Power MIC chip not driving the Gate (pin 5) of the MOSFET in 109B IC properly.

PS: I can understand electronics pretty well

[wildwild]

Originally Posted by MeiTeS

check this solution..check if you not have missing components .. thx Wites for picture..

Already checked and all components are OK.

[wildwild]

Originally Posted by Wites

This is good but 4V can be even if coil is bad so when lcd is connected it must generate around 12V to 16V understand.

Hi Wites,

What should the voltage on pin 4 (Gate of the MOSFET) of the 109B IC be without the LCD connected?

[sohail----]

every thing is ok then go for software ur problem solf

[wildwild]

Originally Posted by sohail----

every thing is ok then go for software ur problem solf

Restored already. Same problem.

[Wites OM Tesla]

Originally Posted by wildwild

Restored already. Same problem.

If coil is open no voltage if coil is short inside 4V if coil is good 4V without lcd.
Man did you replace some component or you chk only under microscope?

[wildwild]

Originally Posted by Wites

If coil is open no voltage if coil is short inside 4V if coil is good 4V without lcd.
Man did you replace some component or you chk only under microscope?

I took measurements and looked under a microscope. It could be a shorted coil. I will replace the coil and see if it was the cause.

[wildwild]

Originally Posted by wildwild

I took measurements and looked under a microscope. It could be a shorted coil. I will replace the coil and see if it was the cause.

UPDATE: I replaced the 6R8 Coil from an old spares and to my surprise the brightness came on

So it must have been partially shorted (measured 0.6 Ohm instead of 0.8 Ohm on my multimeter)



BIG THANK YOU to Wites. You are a LEGEND .



Now I have another problem with another 3GS. It only accepts charge through USB but not through the dock or power adapter. Already tried mainboard in other good housings but same problem.




Thanks all.

[Reinsaddict]

Originally Posted by wildwild

UPDATE: I replaced the 6R8 Coil from an old spares and to my surprise the brightness came on


Now I have another problem with another 3GS. It only accepts charge through USB but not through the dock or power adapter. Already tried mainboard in other good housings but same problem.




Thanks all.

Yep the coil is a strange thing . Told you continuity doesnt mean its working. Glad you fixed it.

For charging look at other Wites fixes in his sticky topic. Truly he is a legend, THE legend.